I think that the Gonzo head was a specific build for that gag -- probably trimmed to that specific twist and never used again. The one cool thing is that once shot, parts of that Gonzo probably ended up in other puppets (since the bodies are typically a separate piece) and the eye mechanism could be cut out and grafted onto another head.
As far as puppets being disposable, think of it this way. Remember in "Total Recall" when Schwarteneggar's head was about to explode towards the end of the film? It changed shape and bulged out the eyes? That wasn't some sort of facial contortion -- it was a special effect head (probably several special effect heads, actually) that were used for maybe 30 seconds in one film, then thrown away (or put in a Planet Hollywood someplace). That's the same way something like Piggy's makeover or Gonzo's nose tweak should be regarded: those puppets were built for a specific shot and gag of a film and then they're discarded. It's really no different than a specially-crafted mannequin for an action sequence or a stuntman that falls off a 20-story building -- at least in regards to filmmaking.