Can't you get centaurified without PoeA though? I haven't tried it (PoeA is more convenient, but it does leave the nagging thought in my head that "this is not a real TF" even though the game pretends otherwise), but I could've sworn that if you get 4 legs and start using horse TFs you can get something centaur-esque.
Oh, I believe you can, but the most thorough way would be the Leitha Charm (or choosing Half-Leithan). I haven't really seen about getting a horse lower body because if I can be a tauric space-lizardbunny, I will be that instead~