I took the bolts and clamps off mine a couple of months ago to adjust them, and they were still in there solid. I removed the hanger bolt on the left side to lower it and was then able to tap it back & forth with a hammer. After hitting it a few times it fell off leaving about 1 1/4 inches of broken tip in the exhaust pipe. It is made of white metal and seemed to be quite corroded & brittle. By tapping a screwdriver in between the broken tip end & the exhaust pipe you can pry the rest out. The same thing happened on the other side. I did not want to replace them just then, so I tapped them back in and tightened up the clamp right at the end of the exhaust pipe and they seem to be holding on OK.
Show us a picture of your new pipes when you get them on. I would like to replace mine with something different in the spring.