RAW it is allowable if you keep the challenge rating the same. The template does not change the creature type so it is still a beast, and a beast is a viable candidate for the template. That being said I would never allow that in my game without some restrictions. If, say, a Dragonborn Druid or Ranger... or perhaps a multiclass Draconic Bloodline Sorcerer/ Bard really wanted to do it for flavor and/or story reasons I would probably homebrew a feat or something to allow it. But to each their own. If you feel comfortable doing it at your table it is certainly RAW (not that it matters much, even if it wasn't RAW you can allow whatever you want). And the game being a one-shot anyway why not go a little crazy. [emoji3]