Originally Posted by MPerson

They can't be welded in, the exhaust isn't that hot to melt the bolt into place, that's what weld is for. The only reason why it may be difficult to get the bolts out is from rust, if you get snowy winters, you'll probably gonna need a breaker bar.
A good idea is to do this on a colder day, or at least not after you've driven, cause the colder the bolt, the more contracted it is, which means less force used to take the bolt out.