After looking through the save editor option list
Well sunnuva gun! I thought the coding for Lapine legs weren't implemented yet! Well, looks like I have to correct that; you actually can create a Bunny-Taur without crashing (I just made a Steele with one, just to be safe). So while in-game will be quite difficult (there is no current method to gain Lapine Legs in-game), you can get to be one through the TiTS Save Editor as
@Alabaster Chimes mentioned.
Take care though with the save editor; its most definitely user-friendly but be mindful of the raw flags and the experimentation.