No I don't mean just the mechanics. The Concept includes personality, character likes and dislikes and everything else. Which is why if someone wants to play a Dwarven Fighter type character (specializing grappling or something) a Bear Warrior is not an option, because the character does not turn into a Bear.
The Personality has to stay the same as the OP wants it to. But that doesn't really come into play much, because 95% of mechanics are separate from the characters thoughts/beliefs/ect.