I have never heard of an exhaust stud being pressed or welded in. It looks per picture there is not enough of the stud to get a vise grip on to it so as stated above weld a nut on it, then heat the flange and turn it out. Might as well remove the other one also, heat the flange first, grip it with some good vise grips, pipe wrench or a stud removal tool. Replace with proper studs and brass nuts.

it's ok to butt heads, just don't do it with a butthead