Is it appropriate to learn the laws of aveilut when both your parents are alive? Or is there a superstition that it could be dangerous to them?
Here it brings the following sources on the matter:
The Chasam Sofer (Shut Y.D. 341) was concerned about it and spoke about pushing off the learning until the coming Tisha B'Av.
Sefer Chassidim (261) is an interesting source. He says you should learn them because they aren't learned generally. So there you have the existing practice of not learning them except when needed, but the Sefer Chassidim not agreeing with it and regarding it as a neglected part of Torah.
R Shlomo Zalman Aurebach was not at all concerned about it, and found it surprising that these Halachos were not learned.
Kenses HaGedola (Y.D. 245:3) writes that the concern is only when it is part of a group study, however privately learning them is not a problem.
When we learned for Smiche, Dayan Zimmermann (The Rov in Gateshead) told us that people should learn Aveilus BEFORE they need it. Otherwise one will make mistakes when it needed.
R' Yosef Berger told me not to learn the latter half of Mo'ed Katan while both parents are living. This was to learn through the sugyas of the gemaras, not just to learn the laws of aveilus, and he said not to. The question I asked him was about if the group I was learning with should begin this topic. He said that it should be done in private. He seems to have held of the Knesses HaGedolah in Yishai's answer.
R' Moshe Heinemann also advises people not to. There is an old "legend" told in Ner Israel, which I never confirmed, that R' Heinemann had a small chabura of 5 guys who wanted to learn hilchos aveilus with whom he began studying. Over the course of a year, 2 or 3 of them had a parent pass away. R' Heinemann cancelled the chabura.