Well I don't know if rust is a big issue for you guys way up north east. For us out west it is not. Mine came off without too much hassle. Gotta love having to get new bolts
My stock headers one of them broke. I was swapping on some headers anyway so didnt even bother with them. You can remove the broken studs and replace them with bolts.
I have a bud in Mi. with 4 stangs and he snaps them often too. It drives him nuts that I (in the desert) have no issues removing mine. I remind him that in Seattle and Alaska, this was not so, and I was in the same boat.
As said, just get new studs or bolts or whatever makes sense.
Did you spray the bolts with any lube prior to heating them? When i put on my o/r H pipe the bolts were rusty. These were 11 year old rusty bolts. We just sprayed the hell out of them with WD-40 and went to work.