@Sancturil
Well, there are many ways to become immortal according to Eastern and Western Lore.
The Philosophers Stone has been through various trails and errors, with the biggest one being sacrificing or Blood Draining infants, in the 100s.
The Peaches of Heavenly Immortality is on the list as a safe way, but not permanent since its a upkeep.
So another one that can be considered a taboo is a racial change. Human to Vamp or Human to Were-creature is bad enough, though were-creatures burn their lifeforce faster for power. So human to Infernal/Celestial is on a list, but that's entirely based on a curse. Kind of like passing skills or a skill that doesn't know death. However, this method turns a person into a pseudo-transcendent. Their using anothers power to get to the next step.
Kind of like using a cheat, and saying your the best. When it's just you BSing everything.