I have replaced the intermediate pipe on 2 saabs. I think the stock middle muffler has pressed in studs that I was able to save on both occasions. You will be better off saving these studs, because they are not easy to drill out due to their being a hardened stud. The nuts will look really bad (corroded), but the threads on the studs will still be sound. To get the nuts off of the stud, I used PB Blaster, then heated the nut red hot using a MAPP torch, and loosened using a chisel and hammer to spin the nut loose. Once the nut has started to come off, chisel or pliers removes it the remainder. This worked half the time as I recall. If the nut doesn't loosen with the chisel, I then carefully cut a segment of the nut off (about the width of the stud) using a dremel with a diamond cutting disc, then heat and chisel to remove/loosen what is left on the stud. I also ran a die down the studs to make sure the threads were clean. If you cut the studs on the front to remove the old flex pipe (Because the replacement has studs attached), expect the cut studs to be very difficult to remove from the front pipe flange as they will be rusted in solid. Heat, hammer and drilling eventually will get them out. It took a few hours each time to remove the old pieces, and the new intermediate (flex) pipe installs very easily.
from the back of the cat. The Cat is a flange, flex pipe has bolts on it that I was able to get off but they were a mess. And really, who even cares if you break them since you're going to drill and put new bolts in.
Never really understood why anyone would design an exhaust system with bolts pressed into the flanges. Flanges with holes with bolts that you can break and replace is so much better.