Don't think studs can be reattached. I "think" those grills are available as reproductions....let us know what you find out.
I have seen them advertized. If you need work done to them you might be better off buying some better ones. Cannot imagine how you can re attach a stud to pot metal.
I know TPP sells repops around $200. Anyone compare those to an original? Mine are originals with some very minor pitting and only one stud is in bad shape; good enough for this driver quality car:TU: