What I mean is would kecleon turn into a ghost type when it is hit with a ghost type move even though it doesn't effect it(while it is still normal type)
Nope. With him being a normal type, it will say that it had no effect...but that's assuming he's still a normal type. If he gets his type changed to something else, then he could become a ghost type since he no longer has the immunity.
It wont be affective because he starts the battle as a normal type so he wont be affective - but you can turn it to another type and then hit him with a ghost type