The only concern I have welding on the new perches is any lube residue catching fire. Not that it would be serious, worst case would be a lot of smoke

The main reason to remove the axles is to swap the studs. I'm going to check with a mechanic buddy to see if they have any trick to installing new studs - they must run across broken studs now and then and may have a method of pulling them in without yanking the axles. Although I think that would be quite a strain on any stud !