Let's be realistic here. Anything can be done if you're willing to pay for it. Powder coating can be very tough, if it is done right. Look at your cooktop, chances are the trays and even the griddles are podwer coated. Those doohickies see a lot higher temps than our engine ever will. Problem is, getting your muffler professional powder coated will cost you beaucoux bucks, probably several times the cost of a replacement muffler. That's if you can find a shop that will bother with a small job like that.

Now if you uncle happen to own a powder coating facility...

There are DIY powder coating kits available, but those are relatively low temp mixes design to cook in the coventional home oven.

If you're that worried about muffler getting gunked up. Buy an addition one and rotating them. Keep one always cooking in antifreeze and swap out the ugly one every so often.