I got my manifold to y-pipe studs out easy peasy with an impact gun, an extension and one of these:
I'm thinking "east coast canada" might have something to do with your experience?
While I don't think it's necessary to change the studs, I do think it's a good idea to have a handful of studs and new nuts on hand prior to doing the job. Some of the studs will be fused to the nut and will turn out of the head instead of turning the nut off the stud. Some will just be stuck...