The stud isn't part of the disc, it goes through into the hub
Just buy a new stud.
Take the wheel off and rotate the hub so the damaged stud is at the rear.
Tap the old one out gently with a hammer and pull the new one in with a wheel nut ensuring it goes in square, make sure you don't over tighten and damage the stud.
Make sure you don't have to hit it too hard, you wouldn't want to damage the hub bearing - it shouldn't be too tight.
I used a ball joint separator to squeeze the old ones out.
Can't remember if you need to remove the disc or not.
I replaced all of mine.