We say the four verses starting "Yehi Shem" (instead of Tachanun) after Shavuot because of the bringing of the Korbanot. Does this have any impact on mourning after Shavuot?
This does not seem to be the ashkenaz minhag to say these verses. Isru chag is kept outside Israel on Friday meaning basically eating a special meal. If anything Isru chag is more important on shvuous since there is no chol hamoed. Also a yahrzeit does not have to fast. In Israel six days after shvuous they dont say tachnun because in keeping with pesach and succos one could still bring the yom tov offerings. Outside Israel one doesnt say tachnun for five days. I am not sure if also one doesnt say on the sixth day after shvuous outside Israel or if a yahrzeit does not have to fast on these extra days after isru chag.