I have a ton of G4 McPony duplicates, and I was thinking about trying to customize them, but their tails really limit the options. Does anyone know if it's possible to re-tail them with new hair and (if it is) where I might find a tutorial on how to do it?
EDIT: And I think we have an answer!
I got looking at the AJ I found yesterday, and I could see glue inside her tail hole. So I ran her under the hot tap for a while to soften the plastic, and then pulled on her tail. It took some muscle, but it did pop out!
I was surprised to see that the hair wasn't simply glued in; it's actually wrapped around a little plastic peg and then glued in. The peg has little... I want to call them prongs, but I don't think that's quite the right word. Anyway, it has pieces on the end to keep the hair in place.
So, assuming all G4 McPonies are tailed the same way as this AJ (a "keychain" one from 2012), it looks like they are indeed re-hairable.
It's worth noting that with my "test" AJ, the prongs on the hair peg broke off when I unwrapped the hair from them. I think the glue might have dried out the plastic. I was flying blind and not being careful, though, so I think someone going into this knowing that the prongs were likely to be brittle would probably be able to unwrap the hair without breaking the peg.