Burning off a nut without hurting the stud is not as hard as it sounds. Assuming the nut is not too small and you have the right tip. You have to be quick so the heat does not transfer to the stud enough for the oxidation process to begin. The rust between the stud and the nut acts as an insulator but only for a few seconds. In most cases the stress on the nut will cause it to snap once you are 2/3 rds the way thru it.

You definitly want to practice on junk first. You want a real challange cut a rusty exhaust pipe out of the inside of a rust muffler without hurting the external muffler pipe

 

I actually did think about heat, but I only have a blow torch, a little propane thing, I was in a rush because its my dd, so bought a cheap shock that came with new stud, took off the shock,lashed out the old one, cut it off and swapped.