1 Broken muffler stud. Should I:
Cut it off flush, drill and tap?
Get a muffler shop to weld on another stud?

The more I break the better engineer I become.

You have lots to work with. Soak it with PB Blaster for a day or two. Then take a pair of vise grips and have a go at it. If it still doesn't budge try a little heat.

?? Is this threaded in? Left hand threads??

That looks tapped..

I say cut it flush and then drill and tap it..

Use a solution of 50%/50% ATF and Acetone and soak it. Then, get one of those stud removers that bite into the stud and try to back it out. Drill and tap last.

With that much sticking out , I'd try the PB and heat also , you may get one good shot at it before the rest of it breaks off. Drill and tap is usually the last resort and also the toughfest to accomplish with hand tools . You might take it to a machine shop and have them do it , if it needs drill and tapped , it's already there at the shop. Your options , good luck ....

Jack / Jaxdream