- Peninei Halakha
One may hold a se’udat mitzva and sing and dance at such a meal, just as one does throughout the year. For example, one may prepare a festive meal for a brit mila, pidyon ha-ben (redemption of a firstborn son), or siyum during the omer period. One who regularly dances and plays happy music at such meals may do so during the omer period, because it is for the joy of a mitzva.
The same goes for hiring musicians: if the local custom is that one always hires musicians for a se’udat mitzva, one may do so during the mourning period of the omer as well. Even though some poskim rule stringently on this matter, the halakha follows those who are lenient, since the halakha always follows the lenient opinion in the case of an uncertainty about a custom of mourning. If, however, it is not clear that people are accustomed to hiring musicians for such events, it is preferable to avoid doing so during this period.
One may celebrate a hakhnasat sefer Torah (inauguration of a new Torah scroll) with music, singing, and dancing, as is customary, because this singing and dancing derives from a mitzva.
The same applies to celebration on the day a boy becomes a bar mitzva or a girl becomes a bat mitzva (that is, on the day of his thirteenth birthday or her twelfth birthday according to the Hebrew calendar): one may celebrate the occasion as one would at any other point throughout the year. When it is impossible to schedule the party on the day the boy actually becomes obligated in mitzvot, one still may conduct a festive meal, but without playing music. If, however, the organizers make sure that someone makes a siyum on the completion of a tractate of the Talmud or an order of the Mishna at the beginning of the party, they may play music as people generally do at bar mitzva celebrations.
 See ma 493:1 and mb 493:3, who write that an engagement party is considered a se’udat mitzva to some degree. Also see above, n. 7. Those who permit playing musical instruments at a se’udat mitzva include: Igrot Moshe, oĥ 2:95, eh 1:97; Mishneh Halakhot 6:109; Yeĥaveh Da’at 6:34. Those who forbid include: Minĥat Yitzĥak 1:111, based on Da’at Kedoshim; see also Piskei Teshuvot 493:5. The halakha follows the lenient opinion when it comes to these laws. Shalmei Mo’ed, p. 454 states in the name of R. Shlomo Zalman Auerbach that one may celebrate a bar mitzva on a different day, as long as there is no band or dancing. Even someone who is confined to a wheelchair or otherwise cannot walk, but whose mind is unimpaired, may not hold a joyous celebration during this period.