Is there any reason I shouldn’t use the top of my JWs Auto Punch to fold a 2oz silver round? Using like a folding die? Will I wreck it somehow?

No problem with that. Just make sure the round is annealed. I have done a 2″ brass round before. You can also pre-bevel the edge of the coin where it makes contact to create a larger surface area. The zinc coating may wear off but that is o.k. The top housing is case hardened and will hold up.