Is there a way to register after using a guest account?

[GregHouse007]

I started the game on a "guest account" several months ago but now I'm thinking that all my "progress" in the game would be safer if I can link it to my email or facebook account, that way I can play the game from my account with any device or I can verify my identity in case I can't enter the game in the future because I lose the device where I play the game.

But when I tried to register with my mail, the system said "only 1 account per device" and didn't let me register. Is there a way I can register on the account I'm already using? or is this not possible by any means?