When they start "deciding for themselves" what they want to be, and how they will react... that's the best thing that can happen to a character.They really come alive that way, and will surprise you in ways that feel totally natural.
In fact, I'm having trouble writing with Hyran because of the pre-set facts in his CS. He tends to become a generally nice-guy if I don't pay attention to my posts, while I had decided on playing a Cerulean (dark personality) @__@; At the moment all my posts feel rather forced, and that is no fun.
So I'd say, roll with it and let yourself be surprised. It's a lot more fun that way!