The muffler assemblies on these bikes are notoriously difficult to remove, so when possible, I simply spray them in place.
I begin with a thorough washing, noting that there's always an accumulation of carbon exhaust deposits on the tips. Some sort of degreaser will take care of that, with a final wipe with a paint prep product, like Dupli-Color cleaner. Often, a light sanding is in order to remove surface scratches.
Next, a precise taping around the perimeter of the tip followed by completely covering the bike to avoid overspray. For this I use large plastic sheet which I source from the dollar store, sold as party table covers. Cut these lightweight sheets into any size or shape you need.
(Below) I also repaint the black pipes forward of the muffler in situ — a real commitment in taping! But, much easier and faster than fighting with muffler removal/install. Here, the pipes are shown in primer.