I've heard they are press in, and I've also heard people just replace them with stainless bolts. I don't know for sure if you can get replacement studs or not.
FWIW, if you get rid of the factory locking nuts and just use regular nuts, and double-nut it, you won't have that problem again. The locking nuts are a distorted thread design and apparently that design doesn't work so well with the heat and rust and they tend to sieze on the stud and then it breaks off. I broke the ends off 3 of the studs on mine before just pitching those and double-nutting it instead.