Is there an issue with doing a “Shloshim ceremony” at the Beis Hachaim during days of no tachanun?
There is no problem with such a ceremony even when tachanun is not said, although if done within 30 days before Yom Tov no hesped or sad speeches should be made. Because of this, many people try to push off the ceremony to a date where this is no longer an issue.
ראה שו”ע או”ח תקמז, ה. משנ”ב סק”ח. שעה”צ סק”ו. ביה”ל ד”ה על המת. שו”ת דבר יהושע ח”ה ליקוטים לג.