Yeah, even if he uses hightemp, it'll bake and flake off. I used 5500 degree paint on my muffler (for looks, was gonna get a Cobra Megaphone but lost budget) and the paint flaked off after the second run.
Even what was black now has mud baked onto it and is now brown. Best thing to do is get out a sander and start sanding it down to bare metal.
Myself, i'm gonna find a baffle from a used muffler at the local salvage yard and piece my custom pipe together.