Yeah, that's my biggest worry. D: Not only do I like keeping them with their original shirts, but I like them keeping their original houses as much as possible. My only exception to that is when they want small items that can go on top things. If they ask for a fish, I give them a goldfish since it has a unique fish bowl. If they ask to replace furniture, I'll ignore it, or if it's something on top of a table, I might do it because it doesn't bother me as much. What gets me is when they change their clothes after talking to other villagers, and then display clothes in their house by replacing something cool! D: Carmen replaced one alpine item so I sent it back, but she replaced a different one with it. I did get her items back, just not in the right places.
I learned to wait until they invite you over, buy the bad item, and THEN mail them the right one as they seem to put it into that spot since it's their "free" one.
Oop, sorry, I'm clogging up your profile. D: