Remarrying divorcee:[1]

It is permitted for one to remarry one’s ex-wife on Chol Hamoed.[2] [Some Poskim[3] however rule that one may not hold a celebratory feast for such an occasion. Other Poskim[4] however rule it is permitted. One may certainly be lenient to hold a feast on the next day.[5] It is questionable whether one may re-perform a Kedushin ceremony during the Moed, if the original Kedushin was invalid.[6]]

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[1] Michaber 546:2; Mishneh Moed Katan 8b; Kitzur SHU”A 104:17

[2] The reason: As a) It does not involve as much joy as a regular marriage. And b) One does not have to place as much time and efforet into the celebration; and c) One is not accustomed to delay such a marriage until the Moed. [M”A 546:3; Tosafus ibid]

[3] M”B 546:7 in name of Beis Yosef

[4] M”B ibid in name of Ashel Avrfaham, Kesav Sofer, Pischeiy Olam

[5] M”B 546:7 and Shaar Hatziyon 546:10

[6] P”M 546 A”A 3