Nidrei Mitzvah-When does a Chumra or custom require Hataras Nedarim?
If one performed a Chumra one time with intent to continue doing so forever it has the status of a vow. If he performed the Chumra or custom three times it is considered a vow even if he did not have in mind to do so forever [and requires Hatras Nedarim to be performed if one wishes to cease the custom]. For this reason, whenever accepting a new Hiddur, Chumra, or custom one is to explicitly state that he is not accepting this upon himself as a vow, and he is only doing so one time or whenever he decides.
A Mitzvah: If one accepted upon himself to perform a certain Biblical or Rabbinical Mitzvah [and not merely a stringency], such as to distribute charity, or learn a certain matter, or perform another Mitzvah, then it is considered a vow [unless he explicitly stated “Beli Neder”]. One is thus to initially state “Beli Neder” upon taking a new Shiur or learning schedule upon himself.
In a pressing circumstance: If a circumstance came up in which it poses difficulty for one to keep his Chumra, Hiddur, or custom, then if it is unusual to accept this Hiddur even in such circumstances, then one is not required to perform Hataras Nedarim. Thus, if one feels weak on an annual personal fast day that he accepted upon himself, such as Erev Rosh Hashanah, he is not required to fast and is not required to perform Hataras Nedarim.
A mistaken custom or Chumra: If one thought that a certain matter was required from the letter of the law and it then became revealed that it is permitted, it is disputed as to whether it is required to be revoked. Practically the custom is to be lenient and not require Hataras Nedarim. Thus if one followed a certain practice due to doubt and later on verified that it is not necessary, it is not required to be revoked. Likewise, if one thought the matter was very severe and then discovered that it is not so severe, he does not require Hatara.
The effect of the Modah-stipulation, performed by Hataras Nedarim on Erev Rosh Hashanah and by Kol Nidreiy: Some opinions rule that those vows which came as a result of following a Chumra or Hiddur Mitzvah, such as one who performed a Hiddur three times, then the stipulation made during Hataras Nedarim [or Kol Nidreiy] is valid to uproot the status of a vow from the Hiddur, even if it does not involve a time of need. [This however only applies if one did not remember the stipulation at the time of performing the Mitzvah. If, however, he remembered the stipulation and disregarding it performed the Mitzvah without saying Bli Neder, the Mitzvah receives the status of a vow.
 See Michaber Yoreh Deah 214:1; Admur 249:13; 161:8; 468:17; Alef Hamagen 581:102; Glosses of Rav Raskin on Siddur [Miluim 25]
 Admur 249:13; 468:17; Nussach of Hataras Nedarim in Siddur; Shaar Hakolel 41:3 [see there for a lengthy discussion of proofs for this matter]
Ruling of Michaber: The Michaber ibid does not state how many times the following off a Hiddur turns the Hiddur into a vow. The Kitzur SHU”A [in previous prints, brought in Shaar Hakolel ibid; Alef Hamagen ibid] questions this wording of the Nussach of “three times” stating that even one time requires Hatara. The Shaar Hakolel ibid answers his questions.
 Michaber ibid; Admur ibid; Alef Hamagen ibid
 Michaber ibid; Admur 161:8 [regarding Netilas Yadayim and other Mitzvos]; 249:13; 468:17 [that if one said Beli Neder it is not binding]
 213:2 [in Michaber regarding learning and in Rama regarding all Mitzvos]; 203:4 and Shach 203:4 regarding charity; M”B 238:5 [regarding all matters of a Mitzvah]
 Meaning that upon performing this Mitzvah he fulfills a Biblical or Rabbinical command, even though he is not obligated to do so at the moment. Such as vowing charity to an institution is a Biblical Mitzvah of charity although initially he was never obligated to pledge the charity to this specific institution. This is opposed to a mere stringency of which its laws were discussed in the previous part of this Halacha.
 Regarding a pledge to give a loan: See Ahavas Chesed Halva 1:11
 M”B ibid
 M”A 581:12; Machatzis Hashekel ibid; Degul Merivava ibid and Yoreh Deah 214:1; Rama 568:2; 581:2 [regarding a Bris during Bahab or Aseres Yimei Teshuvah]; Shaar Hatziyon 568:133 permits in time of need if one cannot find someone to be Matir the Neder; See Piskeiy Teshuvos 568:4
Other Opinion-Opinion of Michaber and Shach: The Michaber 214:1 rules regarding the Hiddur of fasting during Aseres Yimei Teshuvah, that even if one became weak, he is required to do Hataras Nedarim. The Shach 214:2 explains that the reason for this is because only those circumstances that are publicly known not to be included within the Hiddur, such as eating during a Bris Mila during Aseres Yimei Teshuvah, do not require Hataras Nedarim. However, an unexpected circumstance is included in the Hiddur and thus requires Hataras Nedarim. The Degul Merivava ibid argues against the Shach’s explanation, and says the Michaber’s ibid ruling referred to a case that due to weakness the person wanted to revoke his custom forever, and for this everyone agrees that Hatara is required.
 Michaber Y.D. 214:1
 First and Stam opinion of Michaber ibid is that it does not require Hatara. However, he then brings a second lone opinion [Rashba and Ran] that rules it requires Hatara. The conclusion there is that the custom follows the first opinion.
 Conclusion of ruling of Michaber in parentheses.
 Shach 214:5; See Yad Yosef 214:4
 Salmas Chaim 467; Minchas Shlomo 91:20; Yabia Omer 2:30
 Piskeiy Teshuvos 581 footnote 111; See Michaber Yoreh Deah 211:2; Alef Hamagen 581:102; M”B 619:2
Background-Are all one’s future vows invalidatue to the stipulation made by Hataras Nedarim? This depends on whether one remembered his stipulation at the time of the vow. If one remembered the stipulation made during Hataras Nedarim at the time that he said the vow, then the vow is binding and not considered annulled. Furthermore, all future vows from that point and on are considered valid even if he did not remember the stipulation. If, however, at the time of saying the vow one did not remember the stipulation, then in such a case it is considered null and void. Nevertheless, one may only rely on this stipulation to invalidate his vow in a pressing situation. In a non-pressing situation, one must seek a Beis Din to annul the vow. [See Michaber and Rama Yoreh Deah 211:2; Taz 211:3; Nekudos Hakesef; Birkeiy Yosef 228:2; Avkas Rochel 176; Alef Hamagen 581:102; M”B 619:2; Piskeiy Teshuvos 581:17]