Changes in the Amidah applicable to the ten days of repentance:
A. Hamelech Hakadosh:
In Shemoneh Esrei of Aseres Yimei Teshuvah the third blessing concludes with the words “Hamelech Hakadosh” in place of “Hakel Hakadosh”. This begins from the first night of Rosh Hashanah until the end of the ten days of repentance.
Forgot to say Hamelech Hakadosh: If one did not say Hamelech Hakadosh, or is in doubt if he said it, then if he already began the next blessing, he must repeat Shemoneh Esrei. [This applies even by Maariv of the first night of Rosh Hashanah. This applies even if he remembered within Kdei Dibbur of “Shalom Alecha Rebbe”.]
Remembered prior to beginning the next blessing: If he has not yet begun the next blessing, then if he has not passed the amount of time it takes to say Shalom to his Rebbe, [which is the amount of time it takes to say the three words of “Shalom Alecha Rebbe”] then he may say Hamelech Hakadosh and continue. If however he remembered only after this amount of time already passed, then he must repeat from the beginning of Shemoneh Esrei. This applies even if he did not yet begin the next blessings, and certainly applies if he already began the next blessing.
Mieiyn Sheva: On Shabbos Teshuvah, as well as when Rosh Hashanah and Yom Kippur fall on Shabbos, the Chazan recites in the blessing of Mieiyn Sheva recited [after Shemoneh Esrei of Maariv] on Friday night, Hamelech Hakadosh in place of Hakeil Hakadosh. [Likewise when the congregation customarily recites the paragraph of Magen Avos they say the words Hamelech Hakadosh in place of Hakeil Hakadosh.] The Chazan however concludes only with the blessing of Shabbos [i.e. Mikadeish Hashabbos] even if Rosh Hashanah or Yom Kippur falls on Shabbos.
B. Hamelech Hamishpat:
In Shemoneh Esrei of Aseres Yimei Teshuvah the tenth blessing of Hashiva Shofteinu concludes with the words “Hamelech Hamishpat” in place of “Melech Ohave Tzedaka Umishpat”. [This emphasizes that Hashem is the King that is currently in judgment at this time.]
Forgot to say Hamelech Hamishpat: If one did not conclude with ‘Hamelech Hamishpat’, or is in doubt as to how he concluded, then if he already began the next blessing, he is to continue Shemoneh Esrei and is not to go back to the blessing of Hashiva. In such a case it is proper to repeat Shemoneh Esrei [from the beginning] as a Toras Nedava after he concludes his prayers. There is no need to novelize anything in one’s Nedava prayer as is always the rule upon repeating a prayer due to doubt.
Remembered prior to beginning the next blessing: If he remembered prior to beginning the next blessing, then if the amount of time to say “Shalom Alecha Rebbe” has not passed since he concluded the blessing, he is to correct himself and say “Hamelech Hamishpat”. He is then to continue regularly from there. If however this amount of time has already passed, then he is not to correct himself and is rather to continue Shemoneh Esrei as usual. After he concludes his Shemoneh Esrei it is proper to repeat Shemoneh Esrei as a Toras Nidava as stated above.
Hamelech Hakodesh and Hamelech Hamishpat versus Melech Hakadosh and Melech Hamishpat:
One must recite Hamelech Hakadosh and Hamelech Hamishpat with the letter Hei. If one did not do so then some Poskim rule one does not fulfill his obligation. However most Poskim conclude one does fulfill his obligation and so is the final ruling.
If one is in doubt as to whether the time of Kdei Dibbur has passed what is he to do?
If one fixed himself and recited Hamelech Hakadosh but is in doubt as to whether the time of saying “Shalom Alecha Rebbe” had already passed, then he is to continue with Shemoneh Esrei.
If one remembered after saying the word Hakeil, prior to the word Hakadosh, but the time of Kdei Dibbur has passed, what is he to do?
He fulfills his obligation and is to continue with Shemoneh Esrei.
If the Chazan forgot to say Hamelech Hakadosh what is he to do?
He is required to repeat from the beginning of Shemoneh Esrei, just as is the law for an individual. In such a case Kedusha is to be repeated.
If one remembered by Zachreinu or Mi Chamocha that he needs to conclude with Hamelech Hakadosh and is now in doubt as to how he concluded, does he have to repeat Shemoneh Esrei?
Some Poskim rule that he is not to repeat Shemoneh Esrei. Nevertheless if he remembered in middle of Shemoneh Esrei he is to think in his mind from the beginning of Shemoneh Esrei until his current area and then continue verbally from where he left off. [Seemingly however according to Admur and other Poskim it is best to repeat the prayer as a Nedava.]
Hamelech Hamishpat: All the above is only with regards to Hamelech Hakadosh, however regarding Hamelech Hamishpat we do not assume that one recited it even if he remembered to say Zachreinu in the beginning of Shemoneh Esrei. This applies even if he remembered to say Hamelech Hakadosh.
If after Shemoneh Esrei one has doubt as to whether he said Hamelech Hakadosh, does he have to repeat Shemoneh Esrei?
If the doubt entered his mind immediately after Shemoneh Esrei, he is to repeat the prayer. This applies even if he knows that at the beginning of Shemoneh Esrei he intended to recite Hamelech Hakadosh. If however the doubt entered his mind a while after finishing Shemoneh Esrei then if at the beginning of Shemoneh Esrei he knew that he needs to recite Hamelech Hakadosh, he is not required to repeat Shemoneh Esrei.
If in Meiyn Sheva the Chazan said Hakeil Hakadosh instead of Hamelech Hakadosh must he repeat the Meiyn Sheva?
This matter is disputed amongst Poskim. Some Poskim rule if he completed the blessing, then the blessing must be repeated from the beginning. Others rule it is not to be repeated. Practically the Chazan is not to repeat the blessing. Nevertheless if the Chazan remembers prior to saying G-d’s name in the blessing of Mikadeish Hashabbos then he is to go back and say it.
What is the law if one recited Hamelech Hakadosh or Hamelech Hamishpat in Shemoneh Esrei after Aseres Yimei Teshuvah?
One who recited Hamelech Hakadosh or Hamelech Hamishpat during Shemoneh Esrei of after Aseres Yimei Teshuvah, fulfills his obligation, and is not required to repeat Shemoneh Esrei.
C. Zachreinu; Mi Chamocha; Ukesov; Ubisefer:
The Geonim instituted that throughout Aseres Yimei Teshuvah one is to add the following prayers: Zachreinu Lechayim in the blessing of Avos [1st blessing], Mi Chamocha in the blessing of Gevuros [2nd blessing], Ukesov in the blessing of Hodaah [2nd to last blessing], and Ubisefer in the blessing of Sim Shalom.
Forgot to recite: If one forgot to say any of the above additions, then if he already said Hashem’s name in that closing blessing, such as he said Baruch Ata Hashem in “Mechayeh Hameisim”, then he is to continue with the prayer. If one remembered to say it prior to saying Hashem’s name in the concluding blessing [even if he already said Baruch Ata, but not Hashem], he is to say it in the area that he remembers and then continue from where he left off. [In such a case some Poskim rule that one is to say the omitted part at the conclusion of the Amidah after saying the second Yehi Ratzon.]
Bowing by Zachreinu and Mi Chamocha: Some have the custom to bow in Shemoneh Esrei of Rosh Hashanah and Yom Kippur upon reciting the words Zachreinu and Mi Chamocha. See Halacha 6A!
Repeating the words Ukesov and Ubesefer during the Chazan’s repetition:
When the Chazon repeats Shemoneh Esrei, the Chabad custom is that the congregation recites aloud the verses of Ukesov and Ubisefer but not Zachreinu or Mi Chamocha. This applies equally on Shabbos and Yom Tov.
Sparks of Kabala
The stanza of Zachreinu contains exactly eleven words. These eleven words correspond to the eleven Sefiros beginning from Keser. It contains 48 letters corresponding to the names “Eh-yeh Havaya” with the Kolel.
Upon reciting the words “Melech Chafeitz Bachaim” one is to intend to draw eternal life to our souls. Upon reciting “Vekasveinu Bisefer Hachaim” one is to intend to draw a good and long life to our bodies.
Mi Chamocha & Gilgul Neshamos:
On the day of Rosh Hashanah all the souls which require reincarnation into this world [i.e. Gilgul] are judged. This is why the dialect Mi Chamocha, which is added during Aseres Yimei Teshuvah, contains the words “Zocher Leyitzurav Berachamim Lechaim” [remember your creations with mercy for life] and not “Zocher Osanu” or “Zachreinu” [remember us] as is said by the other added stanzas. The reason is because it includes a request of mercy for the souls that will be returned to bodies in this world. It is also for this reason that this stanza was added in the blessing of Techiyas Hameisim [Mechayeh Meisim-resurrection], as it hints to the future life of the souls requiring a Gilgul.
D. Oseh Hashalom:
At the conclusion of Shemoneh Esrei, after Elokaiy Netzor, one says “Oseh Hashalom” in place of “Oseh Shalom”. [This is likewise stated in Kaddish-see Halacha 4. However in Birchas Hamazon the Nussach is Oseh Shalom and not Hashalom. Likewise in the last blessing of Shemoneh Esrei, Sim Shalom, the dialect is not changed.]
 582/1-2; Michaber 582/1
 The reason: The reason for this is because during Aseres Yimei Teshuvah G-d shows his Kingship to the world through judging all his creations. [Admur 582/1; Levush ]
 The reason we are stringent by a doubt: The reason for this is because a person has a Chazaka that he recites his normal tongue. [Beis Yosef; Levush; M”B 582/3]
The reason: As the first three blessings are all considered like one blessing. [Admur ibid; Levush]
Other Opinions: Many Rishonim [Ravaya; Igur; Maor; Raavad] hold that from the letter of the law if one recited Hakeil Hakadosh he is not required to repeat Shemoneh Esrei. Some Poskim conclude that although we do not hold their opinion nevertheless it is proper to join their opinion to other cases of doubt and not require one to repeat Shemoneh Esrei. [See Zechor Leavraham 1 “Shin” and 3 Mareches Reish 138; Kaf Hachaim 582/6]
If one recited Hamalech Hakadosh 90x:
Even if one recited “Baruch Ata Hashem Hamelech Hakadosh” 90x to himself prior to Shemoneh Esrei he still must repeat Shemoneh Esrei in case of doubt. The reason for this is because although in a case of doubt we assume one has said whatever statement he commonly says, which is determined by if he said the statement 90x, nevertheless here since one was never allowed to say Hashem’s name in the blessing 90x it is therefore not considered as if he commonly has said the blessing of Hamelech Hakadosh, as when he now recites Hashem’s name in the blessing he returns to his common conclusion of Ha-kel Hakadosh. [582/3; M”A 582/1; Shalmei Tzibur p. 308; Shaareiy Teshuvah 582/1; Elya Raba 582/4; Chayeh Adam 24/10; M”B 582/3; Kaf Hachaim 582/3]
Other Opinions: Some Poskim rule that if one had recited “Baruch Ata Hashem Hamelech Hakadosh” for a total of 90x prior to the current Shemoneh Esrei then he is not required to repeat if he does not remember whether he said it. [Peri Chadash; Birkeiy Yosef 582/3]; M”E 582/7 rules that since there is a doubt one is to repeat the Shemoneh Esrei as a Nedava.
Initially: One is to avoid initially reciting Hamelech Hakadosh 90x in order to avoid the above dispute. [Kaf Hachaim ibid]
 Implication of Admur ibid and all the other Poskim which have not differentiated between the nights of Rosh Hashanah and the other days. So rules explicitly: Mayim Chaim 22; Kitzur SHU”A 129 in Peas Hashulchan; M”B in Shaar Hatziyon 582/4; Kaf Hachaim 582/3; Alef Hamagen 582/19; Sdei Chemed Mareches Rosh Hashanah 3; Shoel Umeishiv Rivia 3/125; Beis Halevi 1/42; Hagahos Harashash 582; Chaver Ben Chaim 1/33;
Other Opinions: Some Poskim rule that on the first night of Rosh Hashanah one does not repeat Shemoneh Esrei. [Chayeh Adam 24/10; Binyan Shlomo 2/46; Igros Moshe 1/170] The following is the background of this opinion: The Chayeh Adam 24/10 writes in the name of the Gaon Rav Avli Pasvellor that the first night of Rosh Hashanah is similar to the night of Rosh Chodesh on which the ruling is that one who forgot Yaleh Veyavo does not repeat Shemoneh Esrei. Thus if on the night of Rosh Hashanah one forgot to say Hamelech Hakadosh he does not repeat Shemoneh Esrei. The reason for this similarity is because the judgment of Rosh Hashanah is dependent on when is Rosh Chodesh, and since Rosh Chodesh is not sanctified at night, similarly the judgment does not begin at night. [Binyan Shlomo ibid; Igros Moshe ibid] All the above Poskim however negate this opinion. However the Binyan Shlomo and Igros Moshe defend it. Regarding the second night of Rosh Hashanah the Binyan Shlomo ibid leaves this matter in question, although the Igros Moshe ibid rules that one must repeat Shemoneh Esrei.
 Mateh Yehuda; Shaareiy Teshuvah 582/2; M”E 582/9; M”B 582/7; Kaf Hachaim 582/10; Misgeres Hashulchan 129/3 that so is implied from Admur
 Admur 206/3; Kneses Hagedola 206; Olas Tamid 206/3; M”A 206/4; Elya Raba 206/5; Chesed Lealafim 206/3; Ben Ish Chaiy Balak 3; Kaf Hachaim 206/15; 582/9
Other Opinions: Some Poskim rule that it contains four words “Shalom Aleichem Rebbe Mori”. [Beis Yosef in name of Shivlei Haleket; Levush; Taz 206/3; P”M 487]
 Admur 582/2; This applies even if he originally intended to concluded Hakeil Hakadosh due to forgetting that it is Aseres Yimei Teshuvah. [M”A 582/2; P”M 582 A”A” 2; Biur Hagr”a M”E 582/9; M”B 582/8; Kaf Hachaim 582/11]
 Admur 582/1
The reason he cannot just repeat the blessing of Ata Kadosh: As the first three blessings are all viewed as one long blessing. [ibid]
 Admur 582/1; Michaber 582/2
Other Opinions: Some Poskim rule that so long as one has not begun the first word of the next blessing he may say Hamelech Hakadosh. [Kaf Hachaim 582/9; Ashel Avraham Butchach 582 leaves this matter in question] Practically the Poskim negate this opinion. [Yabia Omer 7/51] See Piskeiy Teshuvos 582 footnote 15.
 Admur 582/4; Michaber 582/3 [regarding Shabbos Teshuvah]; Rama ibid [adds Rosh Hashanah and Yom Kippur]
 Seemingly this latter statement is only relevant when Rosh Hashanah or Yom Kippur falls on Shabbos, and hence the novelty is that one does not add Rosh Hashanah or Yom Kippur in the concluding blessing. However on Shabbos Teshuvah there is no reason to think otherwise, that anything else should be added in the concluding blessing other than Shabbos, Upashut.
The reason: The reason why we do not mention Yom Tov [Rosh Hashanah or Yom Kippur] within this blessing of Meiyn Sheva is because its entire reason of being said only relates to Shabbos, as on a regular Yom Tov Meiyn Sheva is not recited. It is recited on Shabbos not due to the holiness of the day [which would thus warrant it to be recited also on Yom Tov] but rather due to Mazikin [damaging forces]. It is thus not similar to the law that requires Shabbos to be mentioned in Niela of Yom Kippur, that although Neilah is never recited on Shabbos and is only recited due to Yom Kippur, nevertheless one is required to mention Shabbos in the Shemoneh Esrei. This is because Yom Kippur obligates four prayers to be recited, which is Shacharis, Musaf, Mincha, and Neilah, and thus one must mention Shabbos in each prayer. However here the blessing of Meiyn Sheva was not instituted due to the holiness of the day [as was Neilah of Yom Kippur] but simply due to the Mazikin. [269/14]
 Admur 582/2
 Admur ibid; Taz 582/1
There is a dispute in Rishonim and Poskim regarding if omitting Hamelech Hamishpat requires the repetition of Shemoneh Esrei. Admur ibid records both opinions and states as follows: Some opinions [Rama 118/1] rule that one does not need to repeat Shemoneh Esrei if he mistakenly said Melech Oheiv. The reason for this is because in these words as well the term king/Melech is mentioned. Other opinions [Michaber 582/1; Rif Rambam] however rules one must return to the blessing of Hashiva and say the proper conclusion of Hamelech Hamishpat, and if he has already concluded Shemoneh Esrei he must repeat Shemoneh Esrei from the beginning. Their reasoning is because the normal wording emphasizes Tzedakah more than Mishpat and during Aseres Yimei Teshuvah one is required to mention and focus on Mishpat and not Tzedakah. Practically Admur concludes “Safek Brachos Lihakel” and therefore we do not return to the blessing of Hashiva Shofteinu. Nevertheless, after concluding Shemoneh Esrei one is to pray again as a Tefilas Nedava. [Admur ibid; and so concludes Taz ibid]
Other Opinions: Some Poskim rule one does not fulfill his obligation and must thus repeat Shemoneh Esrei. [Michaber 582/1; Beis Yosef 582; Rif; Rambam; Rosh; Tosafus; Levush; Peri Chadash 582/1; Birkeiy Yosef 118/2; 582/1; Mamar Mordechai 118/2; Shalmei Tzibur 312] Others rule that one fulfills his obligation and there is no need at all to repeat Shemoneh Esrei even as a Nedava. [Rama 118/1; Darkei Moshe 582/3; Ravaya; Reb Yechiel [brother of Tur]; Hagahos Maimanis; Rashba; Bach; M”A 582/1; Mateh Moshe; Shlah] Practically the Poskim conclude that Safek Brachos Lihakel and one is thus not to repeat Shemoneh Esrei. [Kneses Hagedola 582/2; Elya Raba 582/5; Admur ibid; Chayeh Adam 24/16; Kitzur SHU”A 129/3; Ben Ish Chaiy Netzavim 19; Derech Hachaim 2; M”B 118/3; 582/6; Kaf Hachaim 118/2 and 582/8]
Ruling of Sefaradim: Some Sefaradi Poskim rule that although according to the Michaber one must return to that blessing or repeat Shemoneh Esrei, nevertheless in this instance that there are so many Poskim that argue we apply the rule of Safek Brachos Lihakel even against the ruling of the Michaber. Hence even those of Sefaradic Jewry do not repeat Shemoneh Esrei. [Ben Ish Chaiy Netzavim 19; Kaf Hachaim 118/2] Others however rule that the majority of Sefaradi Poskim agree with the Michaber and hence the Sefaradim are to follow his ruling and return to Hashiva or repeat Shemoneh Esrei. This applies even during the Chazan’s repetition. [Yabia Omer 2/10; 7/51; Piskeiy Teshuvos 582/1]
 Implication in Admur ibid; 107/2
The reason: One cannot repeat the prayer as a Nedava only from the blessing of Hashiva, having it combine with the first half which was valid, as one cannot have the prayer be partially a Nedava and partially an obligation, just like a Karban cannot be half of each. Thus if in if in truth we rule that his first Shemoneh Esrei was valid it ends up that his current blessings from Hashiva are in vain and not a valid Nedava. [107/2]
Other Opinions: Some Poskim rule that one is to only repeat from Hashiva as a Nedava. [Rav Medini in Or Li 30] The Poskim however negate his opinion based on the above. [Yabia Omer 2/10]
 Admur ibid; Taz 582/1
The reason: As according to the second opinion he has not fulfilled his obligation. [ibid]
Other opinions: Some Poskim rule that one is not to repeat the prayer as a Nedava being that a Nedava requires a lot of concentration. [Kaf Hachaim 118/2]
 Admur ibid and 107/1
 Shaar Hakavanos; Elya Raba 582/5; M”B 118/2 in name of Derech Hachaim; Kaf Hachaim 118/2; Admur ibid writes the Hei
 Opinion brought in Elya Raba ibid [regarding Hamelech Hamishpat]; Opinions brought in M”B ibid; Shalmei Tzibur 315; see Kaf Hachaim 118/2
 Peri Chadash 582/1; Machazik Bracha 582/1; P”M 118 M”Z 2; Derech Hachaim 1; M”B 118/2; Zechor Leavraham 118/2; Piskeiy Teshuvos 582/5
 Ashel Avraham Butchach 582
 Daas Torah in name of Daas Kedoshim brought in Piskeiy Teshuvos 582/5
 Zekan Ahron 206; Shalmei Tzibur p. 306; Zechor Leavraham “Shin”; Shaareiy Teshuvah 582/1; M”E 582/8; Ben Ish Chaiy Netzavim 18; Kaf Hachaim 582/5; Or Letziyon 1/13
Other Opinions: Some Poskim rule that the Chazan is not required to repeat from the beginning of Shemoneh Esrei but is rather to begin from Veata Kadosh. The reason for this is because we do not apply the rule that the first three blessings are considered like one blessing with regards to the Chazan’s repetition. [Yabia Omer 1/8; 7/51 based on Meiri Brachos 34a; However see Or Letziyon 1/13 that disputed his ruling]
 Shaareiy Teshuvah ibid; Zechor Leavraham ibid
 Within the Amidah prayer of Rosh Hashanah the prayer of ובכן תן פחדך is added in the third blessing.
 Mayim Chaim 22; Chayeh Adam 28/8; M”B 582/4; Kaf Hachaim 582/6; Beis Halevi 1/72; Galya Misechta 1; Alef Hamagen 582/19
Other opinions: The Sdei Chemed [Mareches Rosh Hashanah] rules that one must repeat Shemoneh Esrei even if he recited Vechein Ten Pachdecha. This is proven from the fact that the earlier Poskim did not differentiate in this matter. [See Alef Hamagen ibid]
 The reason: As we assume since he remembered to add the additional prayer of Vechein Ten Pachdecha certainly he remembered to conclude with Hamelech Hakadosh which is the conclusion of that blessing.[Chayeh Adam ibid] Alternatively there is a true doubt involved in this case as we cannot assume he said the wrong Nussach being he said Vechein Ten Pachdecha, hence we apply Safek Brachos Lihakel and he does not repeat Shemoneh Esrei. It cannot be repeated as a Nedava as we do not Daven a Nedava on Yom Tov. [Galya Misechta ibid]
 Ashel Avraham Butchach 582
 The reason: As perhaps since he remembered to add the additional prayer of Mi Chamocha he also remembered to conclude with Hamelech Hakadosh, and hence the matter is a true doubt. [ibid]
 As according to some Poskim [P”M 62 M”Z 1] thinking the prayer is valid in a case of “Ones”. This then creates a Safek Sfeka which exempts one from needing to repeat Shemoneh Esrei even as a Nedava. [Ashel Avraham ibid]
 As the Peri Chadash 62 and 94 rules that thinking the prayer is invalid even in a case of Ones and he hence in this case there is only one Safek. So is also implied from Admur 62/3 that one does not fulfill his obligation at all through thinking the words, unlike the P”M ibid.
 Ashel Avraham ibid; Thus according to Admur it would be proper to repeat Shemoneh Esrei as a Nedava while according to the Michaber one would be required to repeat Shemoneh Esrei.
 Or Li 111; Yabia Omer 7/51-3
 M”B 114/38 [regarding Mashiv Haruach and Yaaleh Veayavo]; Piskeiy Teshuvos 582/2
 See Kaf Hachaim 582/18; Mateh Efraim 582/5; Alef Lamateh 582/1; Alef Hamagen 582/17; Piskeiy Teshuvos 582/6
 M”B 582/10
 Kneses Hagedola 582/5; Elya Raba 582/2; Mateh Yehuda; Mateh Efraim 582/5; Shalmei Chagiga in name of Mahariy Iash [brought in Alef Lamateh ibid]; Machazik Bracha 582/3; Shalmei Tzibur 197; Zechor Leavraham 3/143; Shaareiy Teshuvah 582/3; Ben Ish Chaiy Netzavim 18 The reason: The Chida in Machazik Bracha explains that according to Kabala there is a mystical reason behind reciting Meiyn Sheva and hence it must be repeated if not recited properly. [Kaf Hachaim ibid]
 If however he did not yet complete the blessing then he returns to the words Hamelech Hakadosh and reads from there and onwards. [ibid]
 Peri Chadash [brought in Kaf Hachaim ibid]; Gan Melech 149; Siddur Derech Hachaim; Peri Megadim 582 A”A 2 ; Nishmas Adam; Yeshuos Yaakov; Pischeiy Teshuvah in name of Divrei David 55; Alef Hamagen 582/17; Kitzur SHU”A 129/4
The reason: As the entire blessing of Meiyn Sheva is only recited use to Sakana, and hence we do not require its repetition if a mistake was made. [Peri Chadash ibid]
 Likkutei Mahrich; Luach Eretz Yisrael; Piskeiy Teshuvos 582/6; The Kaf Hachaim ibid concludes that one who does not repeat the blessing is not to be protested, although it seems he leans like the stringent opinion viewed by the Chida, based on Kabala. See Yabia Omer 2/29.
 M”B ibid; M”E ibid; See Peri Chadash ibid that “although if he is still within Kdei Dibbur we protest him and make him return”. Vetzaruch Iyun as to which part of the prayer he is referring to Kdei Dibbur of? The words Hakeil Hakadosh or the concluding blessing.
 Olas Tamid 118/2; Bach 582; Kneses Hagedola 108/6; Elya Raba 108-end; Peri Chadash 582/1; Mateh Yehuda; Beir Heiytiv 108/1; Birkeiy Yosef 118/3; Machazik Bracha 582/2; P”M 118 A”A 1; Beis Oved 118/5; Shaareiy Teshuvah 108/1 [that so is the ruling of most Achronim]; Derech Hachaim 33/46 and 72; Kitzur SHU”A 129/3; Mishneh Berurah 108/1; Ketzos Hashulchan 21/4; Kaf Hachaim 118/3
Other Poskim: Some Poskim rule one is required to repeat Shemoneh Esrei. [Rame in Alfasi Zuta end of Brachos, brought in Machazik Bracha ibid] Other Poskim conclude that it is best to repeat Shemoneh Esrei as a Toras Nedava. [Mamar Mordechai 118/2; Shalmei Tzibur 122; Beir Heiytiv ibid in his understanding of Taz 582/2; Peri Chadash ibid concludes if one repeats Shemoneh Esrei as a Nedava he is blessed. See Shaareiy Teshuvah ibid]
Opinion of Taz: The Beir Heiytiv ibid learns that according to the Taz 582/2 which rules one must repeat Betoras Nedava during Aseres Yimei Teshuvah if he said the wrong Nusach in Hamelech Hamishpat, similarly if one made a mistake during the rest of the year he is to repeat the prayer as a Nedava. However the Shaareiy Teshuvah ibid negates this suggestion saying the Taz was only stringent by Aseres Yimei Teshuvah when we want to fulfill our obligation according to all.
Opinion of Admur: Admur 582/2 rules like the Taz in 582/2 that during Aseres Yimei Teshuvah one is to repeat the prayer as a Nedava. Thus there is room to learn in his opinion as learns the Beir Heiytiv ibid, that also during the year if the wrong Nussach was recited one is to repeat the prayer as a Toras Nedava. Practically however the Ketzos Hashulchan ibid rules it is not to be recited and that so is implied from Admur 108/18 that only when one has stated a lie must the prayer be repeated. Likewise the Nesiv Hachaim, which wrote glosses on the Derech Hachaim according to the opinion Admur, does not record any dissenting opinion of Admur in the above. Hiskashrus Yom Kippur likewise writes one is not required to repeat Shemoneh Esrei.
 Correct pronunciation of Zachreinu and Kasveinu: The word Zachreinu and Kasveinu is stated with a Kamatz under the Zayin [Zachrein; Kasveinu] as this is the form of a request from G-d. It is not stated with a Cholam-Zochreinu/Kosveinu- as this is a mere statement that G-d is our remembrance and not a request. [Levush; Mateh Moshe 796; M”A 582/4; Omitted in Admur in SHU”A, although this is the Nussach in the Siddur]
 Correct pronunciation: One is to recite the word Lechaim with a Shva under the Lamed-Lechaim- and not with a patach under the Lamed [Lachaim]. The reason for this is because it sounds like one is saying “Lo Chaim” which means “no life”, and during these days [of Aseres Yimei Teshuvah], which are days of judgment, one must be particular in expressing his requests properly. However during the rest of the year we state Lachaim [Vehamideinu Malkeinu Lachaim] with a patach and we do not suspect for a mispronunciation as [G-d] follows the persons intention behind the word. [582/7]
 During the week the Nussach is Av Harachaman. However during Musaf, Mincha of Shabbos and Neilah the Nussach is Av Harachamim. [Siddur Admur; Peri Eitz Chaim Shaar R”H 6; Shaar Hakavanos 96b; Shaar Hakolel 9/7; Kaf Hachaim 582/34; Darkei Chaim Veshalom 710; See Likkutei Mahrich 62b; ] Rachaman refers to Z”A while Rachamim refers to Ava. [Likkutei Torah R.H. p. 62]
 Admur ibid; Michaber 582/5 regarding Zachreinu and Mi Chamocha; Rama ibid regarding Ukesov and Besefer; Rosh Brachos Perek 1; Ramban; Ran; implication of Rambam 2/10; Terumas Hadeshen 144; Levush; Bach; Kaf Hachaim 582/27
One is not to recite it as soon as he remembers and is not to repeat the blessing from the beginning. Doing so is forbidden due to it being a blessing in vain as these additions are merely an institution of the Geonim. [Admur ibid] One is not to conclude the blessing with Lamdeini Chukecha and then repeat it with the added verse. [Ruach Chaim 582/2; Ben Ish Chaiy Netzavim 20; Kaf Hachaim 582/31; see Shaareiy Tziyon 188/18] One is not to recite the verse prior to beginning the next blessing. [Elya Raba 582/11; Kaf Hachaim 582/30; Ben Ish Chaiy Netzavim 20; Yabia Omer 1/22; See M”B 114/32] One is not allowed to be stringent upon himself and repeat the blessing. [Darkei Moshe 582/4; M”A 582/4; Admur ibid] One is not to repeat Shemoneh Esrei even as a Nedava. [Machatzis Hashekel ibid; Kaf Hachaim 582/28]
Other Opinions: Tosafus [Brachos 12b] rules that these additions have the same status as Hakeil Hakadosh and hence if it was omitted one must return to that blessing or repeat Shemoneh Esrei. Practically most Rishonim and Poskim do not rule like this opinion. [See Kaf Hachaim ibid] Some Poskim rule that if one did not yet begin the next blessing he may say the omitted part after concluding the blessing prior to beginning the next blessing. [Ashel Avraham Butchach 582; Alef Hamagen 582/25] However many Poskim argue on this allowance and hold that doing so is considered an interval of the prayer. Thus one is to continue with the next blessing. [Simple implication from Admur and all other Poskim ibid and so rules Elya Raba 582/11; Kaf Hachaim 582/30; Ben Ish Chaiy Netzavim 20; Yabia Omer 1/22; See M”B 114/32]
 Kaf Hachaim 582/31
 One is not to go back and say it in its original place and then repeat from there. [implication of Admur ibid which states ”Bimakom Shenizkor”; Mateh Efraim 582/10 [regarding Ukesov]; however see M”E 602/8] So rules Admur also in 114/7 [regarding Mashiv Haruach]; However see 294/7 regarding Ata Chonantanu that one is to repeat from Vechoneinu Meitcha.
The reason: The reason for why one is not to go back to the original area is in order so one not repeat G-d’s name. [M”E ibid] To note however that this would only explain the stanza of Ukesov [which requires repeating from Vechol Hachaim] and not the other stanzas. Vetzaruch Iyun.
Other Opinions: Some Poskim rule that one may go back to the area of the addition and then continue from there as usual, and not from where he left off. This applies even though he may need to repeat the names of Hashem in that blessing. [M”B 582/16; P”M 114 A”A 8; 582 A”A 4; Ashel Avraham Butchach 582 Tinyana; Sdei Chemed Mareches Rosh Hashanah 3/3; Alef Hamagen 582/26; Kaf Hachaim 582/31] There is no worry of having to repeat Hashem’s name upon going back as one is not saying it as a blessing but simply as a supplication. [ibid]
 Kaf Hachaim 582/27 and 32; Ben Ish Chaiy Netzavim 20 [in name of Torah Leshma] writes that the verse of Zochreinu Lechaim is to be recited in Shomeia Tefila, although on Shabbos and Yom Tov one recites it prior to the second Yehi Ratzon. However Mi Chamocha is not a request and is hence not to be recited if it was omitted. The verse of Ubisefer is to be recited prior to the second Yehi Ratzon. The Kaf Hachaim 582/32 concludes that from other Achronim it implies that all the verses may be recited prior to the second Yehi Ratzon.
 Igros Kodesh 3/5 based on Rebbe Rayatz [brought in Shaareiy Halacha Uminhag 1/241; Shulchan Menachem 3/92]; Bnei Yisaschar Tishrei 2/23; Taamei Haminhagim 603 in name of Rav Sar Shalom of Belz; Mateh Efraim 584/10 [only mentions Ukesov and Bisefer]; See Otzer Minhagei Chabad 189
The reason: The last two stanzas of Ukesov and Ubisefer are requests from G-d and hence are befitting to be said by the congregation. However the stanzas of Mi Chamocha is a statement and not a request. Likewise the first stanza of Zechor is of lesser quality in comparison to the request the congregation recited in their private prayer of Ukesov and Ubisefer, and is thus not befitting to be said. [Rebbe ibid]
Other customs: Some communities are accustomed to recite aloud all four stanzas prior to the Chazan. [Likkutei Mahrich 68a; Yalkut Avraham 602; Piskeiy Teshuvos 582/8] Others are accustomed not to repeat any of the verses during the Chazan’s repetition. [custom of Gr”a Maaseh Rav 204]
 Siddur Admur; Baal Haturim; Shaar Hakavanos p. 96; Kaf Hachaim 582/33
 Siddur Rashash; Kaf Hachaim ibid
 Shaar Hakavanos ibid
 Siddur Rashash ibid
 Shaar Hakavanos p. 97; Kaf Hachaim 582/34
 Siddur Admur [omitted in Shulchan Aruch]; Shaar Hakavanos 190; Peri Eitz Chaim Shaar R”H 7; Kaf Hachaim 582/15; M”E 582/1 and 22
The reason: The Gematria of Hashalom is the same as Safriel Hamalach which is the angel which writes the Jews in the book of life during Aseres Yimei Teshuvah. [Peri Eitz Chaim ibid brought in Kaf Hachaim ibid; M”E ibid] In however Hagahos Mordechai [Miseches Rosh Hashanah 720 he states as follows: Safiriel is the Gematria of Oseh and Oseh is the Gematria of Hashalom. Alternatively this hints to the kindness of Hashem that swerves the judgment to merit in a case that the sins and merits are equal, and the verse states “Maaseh Hatzedaka Shalom”.
 Hisvadyos 1984 1/28 [The Rebbe stated that he asked this question to the Rebbe Rayatz, and after a discussion on the matter the Rebbe Rayatz replied that one is not to swerve from the dialect written in the Siddur.] See also Kuntrus Hasiddur [Hakdama] that this question is raised.
 Siddur Admur does not change the Nussach of Sim Shalom during Aseres Yimei Teshuvah or Rosh Hashanah. This follows the custom of the Sefaradim brought in Shalah [Tefilas Rosh Hashanah] that one may not change the dialect. The Shaar Hakolel 9/35 states that those that change the dialect of the concluding blessing of Sim Shalom to “Oseh Hashalom” [see custom of Ashkenazim] are changing from the dialect of the Sages and transgress the prohibition of “Lo Sisa” [not to say Hashem’s name in vain]. Likewise the concluding blessings in Shemoneh Esrei all contain 113 letters corresponding to the 113 words in the prayer of Chana, and they thus swerve from this institution by changing the concluding blessing.
Ashkenazi custom: The widespread custom of Ashkenazi Jewry from the times of the Rishonim is to conclude the blessing of Sim Shalom with “Besefer Chaim….Baruch Ata Hashem Oseh Hashalom” instead of “Hamevareich Es Amo Yisrael Bashalom”. This is followed through Aseres Yimei Teshuvah. [Artscroll Siddur]