Shalom, My fathers custom is to daven nusach Ashkenaz but I always wanted to be a chassid so I switched to nusach sefard, then later on I learned that the ar"i said that nusach sefard defiantly breaks through into shamayim. And I’ve been davening sefard for a long time now, and I’m very used to it, but my fathers minhag is to daven Ashkenaz, should I continue davening sefard or should I go back to nusach Ashkenaz? Thanks so much for your time!

Shalom, Thank you for your question. There are really two issues at hand here - firstly, whether one is allowed to change their nusach, and secondly, whether this interferes with the mitzvah to honor one's parents. There is much written on the question of how it is possible that anyone ever changed from Ashkenazi nusach to the sefard nusach. Rav Feinstein zt"l writes that he does not understand at all who permitted this, and he rejects the numerous attempts to justify the change. He concludes by saying that "nonetheless we do not question those who made the change, for they must have had a reason that allowed them to make this change" (Igrot Moshe, Orach Haim 2, 24). Others though have ruled that this change is valid (perhaps not surprisingly, great Hassidic poskim such as the Teshuvot Divrei Chaim 2:O.C.8). Perhaps the most valid reason to make this change would be if one were to permanently move to be part of a Hassidic community, for in that case we rule that anyone who moves to a new location takes on the customs of their new venue. I believe that today "moving" communities can be achieved by association with a different synagogue or Rabbi, even if one's address stays the same. So, from this point of view, if you truly do become a Hassid, and in all your service of Hashem associate with a Hassidic movement, it would seem that according to most opinions you could make the change in nusach also. However, we still need to examine if this might be a slight to your parents, and a breach of honoring them. I see that you are still in high school, and so this might be an even bigger issue than for a married child who has left home and whose nusach change might not even be noticed by their parents. There is a halachic discussion as to whether issues such as this are part of honoring one's parents - but all agree that the right thing to do is to make sure that one's parents are happy and proud with what their children do, and to avoid any arguments [of course there are limits to this, but the general idea is clear]. So, my advice is to have a talk with your father about this. See if he has any problem with you changing nusach. If he does not like the idea, for any reason, then I would advise you to go back to Ashkenazi nusach while you live at home, until you move out to your own community or home. But if your father approves, then you may continue with the nusach sefard you have taken on. Blessings.