I would imagine that there is more to the graft than simply pouring blood into a wound. Potions and spells of Regeneration do not alter the physiology of the beneficiary. However, having a troll shaman perform the ritual rather than simply casting Regen or Monstrous Regen seems to have made a difference.

Possibility: Serini was dead when the healing was performed, and is now a troll with Serini"s memories. Instead of Serini"s soul, the body is inhabited by a troll soul that believes it is Serini.

However, that aside, using reagents of various types doesn't change the person using the potion. Use all the fairy dust you like, your character may fly or turn invisible, but doesn't turn into a half-fairy freak. Something else is at work.