-On what pawns can be mutated: Any colonist that can be ordered to prioritize work (non-ghoul, not in mental break. Children allowed). The mutation happens on whoever activates the mutation, so it's impossible to forcibly mutate other pawns (downed, prisoners, enemies or visitors). Such is detailed on the Twisted Monolith article.
-Can cure Gutworms if the result of mutation is a Fleshmass stomach.