I think you are all missing the point here.
There's one less kran and one more enki, we should all be celebrating

Fun fact: Not only was this a species change, it was also a sex change!
Okay, now that I am done with that. Sure, you should stay within the settings but, if a player really wants to try something new I don't see anything wrong with going into the "far fetched" category. I mean, to be honest, this is how I went -
Waylander Ylian - scrapped
Druss Kran - scrapped
Cadoras Enkidukai - later became Nurahk
Nostra Ynnwn - later became part of Nurahk's soul
Armeen (can't remember) - later became part of Nurahk's soul.
Nurahk is the soul of the son of Cadoras/Armeen/Nostra (Cadoras being the host and the other two being souls) and Shauri - he is also the adopted son of Sangwa. With this reasoning he is nobility in the House of Purrty. I've never actually approached Lolitra with this, deciding instead to basically deny it. He used to have two souls (Nostra and Armeen) passed on from Cadoras.
I've decided to scrap most of his history. Changed it to "Nurahk used to known as Cadoras, during his time under this name he had two servants, Nostra and Armeen. Basically puppets. Cadoras became mentally unstable and developped multiple personality syndrom, believing that the two servants he once controlled were now seperate souls within his body. He lost all his memory one day and decided to be known as Nurahk (around here he started believing he was his own son) from then on, the multiple personality syndrom has since disappeared."
I'm not saying you should godmod and I'm definitely not saying I didn't make mistakes in my character development. But keep in mind it is a game and the player may want to try something new.
Cheers.