I replaced donut hangers, when I installed a Brabus Exhaust. (more) ....
As Bruce mentioned, it is a real Pain, actually the hardest part of the install of my exhaust. I had the car up on ramps, and put the two new donuts on first, I had to spray them with Silicon Spray to get them to slide into the hangers. I then used some wide cable ties, around the donuts, and used locking pliers to pull the donuts down (and out) so that I could get them under the hanger for the muffler. I was afraid that a hanger, or thin cable tie would rip the donuts. Since I had the new muffler not 'connected', I had the luxury of being able to angle the muffler to get one of the donuts on easier than the other. After I got the second donut on, I then connected the muffler.