You can keep your Grafts and obtain new ones. Grafts are not Magical Items, they are limbs and organs made to work with your body by magical means. So unless you are trying to say VoPers must forgo casting Regeneration to recover lost limbs and need to immediately commit suicide because their organs have a black market value (which would be pointless, souls have a gold value) it's retarded to classify them as such.
Graft usage is entirely subjective to flavor. Like nothing in VoP or Voluntary Poverty excludes their usage. "desecrating corpses" for new Grafts is a Christian belief that has absolutely nothing to do with Alignment mechanics. In fact, we are discussing BoED here. You could hang a Demon's head in your den as a hunting award assuming your Evil-Only "poison" doesn't rot it away and it'd probably help you'd qualify for the Saint Template. What you should avoid is having your character place wealth into the Graft. You don't walk up to a store and buy it with the gold you saved up. You butcher the corpse it's self and behold it's body in awe, seek to improve and better your self.
You should also avoid Fiend Grafts. Yeah you can fluff it as redeeming them or w/e. But seriously, a daily DC 15 Will Save or break VoP? So not worth even the chance you're debuffed enough to have a 5% chance of failure. You'd lose within a month.
