That's a good question

I do know that if you have a small or medium shop & want to replace it with a superior shop, that you can destroy your existing building & replace it without disturbing the vendors inside.
If you're on Rk1, I've got a pretty good supply of serums if you need. If you do have a smaller market, perhaps you could build a superior shop & try placing it with the existing one still there, then do a replacement if that isn't allowed.