Kiddush Levana:

One does not recite Kiddush Levana prior to Yom Kippur.[1] It is rather to be recited on Motzei Yom Kippur.[2]

Eating and changing clothing before Kiddush Levana on Motzei Yom Kippur:[3] When reciting Kiddush Levana on Motzei Yom Kippur, one does not need to eat prior to saying it, as one is already in a joyous mood.[4] [However, one should wash his face[5] and switch his shoes beforehand.[6] One is to recite Havdala prior to Kiddush Levana.[7] One recites Kiddush Levana while still wearing a Gartel.[8]]

Q&A

If switching shoes on Motzei Yom Kippur prior to Kiddush Levana will cause one to miss saying it with a Minyan, what is he to do?[9]

He is to say Kiddush Levana with the Minyan.

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[1] Rama 426/2; 602/1; Seder Hayom; Levush 602/2 that so is the custom; M”E 602/46; Mishmeres Shalom 41/1; Sefer Haminhagim p. 126 [English]; See Otzer Minhagei Chabad p. 249; omitted from Admur 602 Vetzaruch Iyun!

The reason: It is not to be said before Yom Kippur because one is in a state of pain due to it being a time of forgiveness of sin. [M”A 426/5] Others write as follows: It is not to be said as one is in a state of seriousness due to the days of Judgment and he is thus not in a state of joy which is required for the recital of Kiddush Levana. [M”B 426/9]

Other Opinions: Some Poskim rule that one is specifically to say Kiddush Levana prior to Yom Kippur, as perhaps this merit of saying Kiddush Levana will turn the judgment to the side of good. [Gadol brought in Levush 602/2; Elya Raba 602/7; Beis Meir 426; Biur HaGr”a 602; Chida in Moreh Baetzba 9/283 and other Poskim brought in Kaf Hachaim 426/27; 602/19; M”B 602/10; Biur Halacha 426 “Velo Kodem Yom Hakippurim”; Makor Chaim 602; Nemukei Orach Chaim 602; Alef Lamateh 602/25; See Otzer ibid]

[2] The reason: As on Motzei Yom Kippur one is in a state of joy. [Rama ibid; See 623/14; 624/9 that Motzei Yom Kippur is a Yom Tov.]

[3] M”B 426/11

[4] Chayeh Adam 118/15; M”B ibid

Other opinions: Some Poskim rule one is to eat beforehand. [Mateh Efraim 624/4]

[5] Luach Kolel Chabad

[6] Luach Kolel Chabad; Piskeiy Teshuvos 624/1; The Rebbe switched his shoes beforehand. [Reply of Rabbi Groner in correspondence]

Other customs: Many are accustomed to recite it immediately after Davening, even prior to changing shoes. [Nitei Gavriel Yom Kippur 66/15 footnote 23]

[7] Sefer Haminhagim p. 126 [English]; Likkut Dinei Rosh Chodesh 12/13

The reason: Perhaps this is because Havdala is more Tadir. [see Poskim in 681 regarding Chanukah]

[8] Sefer Haminhagim p. 126

[9] See Shaar Hatziyon 426/9 based on Elya Raba; Mateh Efraim 624/4