I have yahrzeit in Adar Rishon. The shul I attend proposes to change the custom of the last 70 years (when it was established) so that any Adar yahrzeit will be observed in Adar Sheini in a leap year. Is there any accepted halachic basis for this?
If the family member in question passed away in Adar I of a leap year, the yahrzeit must be observed in Adar I, and not in Adar II.
However, if the family member passed away in an ordinary year, there are two opinions as to when the yahrzeit should be observed, Shulchan Aruch maintaining that it is observed in Adar II, and Rema writing that it is observed on Adar I, and adding that both months should be observed. There is therefore halachic grounds for observing the yahtzeit on Adar II, but the best would be to observe both months (as Mishnah Berurah also recommends). You could fast (if this is your custom) and say kaddish on both, and learn mishnayos/go to the kever, and the shul would surely not object.