The Pro hunter frame will accept any barrel. However the forearms are different for the rifle, pistol and muzzleloader barrels. Butt stock is the same for rifle and muzzleloader and pistol grip is obviously different. I'm thinking that possibly a shotgun barrel would require a separate forearm too but not sure.
With my frame I shoot a 7mm-08 rifle, 45 cal muzzleloader then I switch to pistol configuration and shoot a .243 Win or a 50 cal muzzleloader pistol.