For the Grafting part, the RMSS/FRP Construct Companion includes the Chengeling list(s). I'm pretty sure you can take inspiration from it, since it seems to deal exactly with what you want (you can also get ideas from the Amalgams list, though that one deals with dead parts cobbled together and given a semblance of life - but the technical details might be worth it).
Depending on the setting, I would make such a caster a pure Essence, E/C hybrid, or pure Channeling - or even Arcane if this seems too far removed from standard magic in the setting. Depending on the other base lists you assign, I would use Animist, Druid, Sorcerer or Alchemist as a template for skill costs. Channeling types would be inspired either by a god (probably not a 'good' one, since creating abominations is hardly orderly, but not necessarily straight evil) or by an unfathomable alien entity (I can really see an Elder God-like entity 'inspiring' people to research into creating abominations to change the biome of the world). Essence and Arcane types would be self-sufficient but research oriented, either from a zoological or from a magical point of view. The hybrid might be a researcher with a big philosophical question such as 'can man give the spark of true life - a soul - to a creation', and his chimaera are essentially milestones on the way to the great work, but since it deals with the spirit as much as the body, having a hybrid is preferable in my opinion.
An E/C hybrid could also merge living beings (animals, humanoids...) with that of corporeal planar entities such as demons to create planar hybrids, or try to infuse animals with elemental matter to create elemental hybrids (that would be more in the realm of a pure Essence or Arcane caster, probably, though). Once again, I think you can get a wealth of ideas from the Construct Companion.