2 possible options.

Drill, tap insert stud and or locktite a helicoil to restore original diameter- or dual size/ended stud.

Have an electric welding shop DISCONNECT YOUR BATTERY TERMINALS and tack a piece of rod to the remaining stud to use as a ground attachment, then weld a new piece of bolt or stud to existing shift selector rod. Remove tacked on ground rod and grind down tack area if needed.
Check shift selector motion to insure welding did not fuse any internal shifting linkage.