When you enter the appearance modifier, you can still "interact" in the outside world. This includes mounting up. Until next week, if you mount up whilst modifying your character's body type and exit after applying the changes (you do have to apply; you can't just exit after changing the sliders and doing nothing else), you will find that your appearance has changed a little bit more than you could have possibly imagined, as Calphaya demonstrates.
|Isn't she a majestic sight?|
Sadly, this isn't permanent. Any cast of any sort would cancel this out, and I'd imagine the same would be true of travelling. Also, if you want to make the most of this before next week, you'd need to have a fair amount of Cartel Coins (80 per temporary transformation).
Still, this is definitely the funniest glitch I've come across for a long time now.