Should you change for someone you love?

Okay I know a lot of people are going to say "just be yourself, your beautiful the way you are blah blah blah"and I know that. That's not what I'm asking.When your in a relationship you change anyway, normally at the same rate the other person is, right? Everyone changes over time, but how much is too much? What are reasonable changes to make? And what are unreasonable ones? For example I've changed dietary habits, went back to school, and changed other things about the way I live at my fiance's suggestion with no objection. I'm just wondering what you would consider to be an unreasonable change if someone asked. Is giving up school too much? giving up friends? giving up on a career?...etc. This is just hypothetical really, just looking for some opinions.