Speaking from many, many years of experience, changing out rusty bolts for the fun of it ranks up there as one of the worst ideas ever. You didn't say what bolts, but chances are some of those are from 1984 or 1985. Guess what happens when you remove them? You end up with 2 pieces, one of which is still firmly planted in the hole. The other piece in your hand is no longer holding whatever it should have been holding.