Let's say you asked your old rabbi a question and he answered you, but now let's say you have lost contact with him. Do you still have to follow this pesak or can you change?
If you change rabbi/shita/chasidis - you take on the laws of the new.
EG - ashkenaz woman marries sfardi - eats rice on pesach Askenaz turns sefardi - change your tefilin If your new rebbi only holds R Tam lechumra, you should not hold it lekula in his town.
If you learn a sugya/halacha or anything wrong, or differntly later - you change. Judaism is a living organism