Changes in diet can come just by respecting your girlfriends tastes... my girl doesnt like sushi much but loves vietnamese soup (pho). So I tend to eat pho more often then sushi now... no big deal really, I like both foods pretty well
Changes in clothes? Nah, my girl occassionally grabs a shirt or a pair of pants she sees that she likes, but thankfully she realises I can't dress like a backstreet boy or I will kill myself. So she only buys clothes she knows I like... well, she wont buy me my boots cuz she don't like them too much ("you look like a gangsta!" me - "how can I look like a gangsta? I'm white!" hahaha)...
I hang out with her friends a bit now (they are pretty good people), I watch more girlie movies then ever before (how ot lose a guy in 10 days... etc.).. but fundamentally nothing is different except that I am much happier...
It's already been said in this thread I think, but if she wants to change your fundamentals, then she isnt attracted to you, she is only attracted to the *idea* of you. You being the male she is going to mold into the perfect man for her. Which is absolute scheisse!