Everyone who believes Luffy will be kinda possessed by the Spirit of Joyboy has to wake up.
On a narrative standpoint Luffy will always be Luffy there is not even a tiny possibility.
Luffy is the core principle of a personality you can't change, he's unbendable. His willpower is not a single inch bendable.
So please forget those ideas about Joyboy possessing Luffy or Luffy will change.
This would be a waste of 1043 chapters and decades of writing, even a C-Tier Autor wouldn't make such fatal errors. Oda ain't that stupid.
I guarantee you this will never ever be the case. Not in the slightest, never ever will this happen.
In all of One Piece after 1000+ chapters the vent that most definitely will never be the case is Luffy changing his personality or being possesed.
Stop it, it won't happen. Just read One Piece unterstand Odas main principles and cores of the story, and you won't even think about something like Luffy being possesed by Joyboy or changing personality. That's commonsense