if there was a way you could change someones personality with high success then someone would have made it a billion dollar business already.
the main concern I see in trying to be positive is that you would need some kind of positive feedback from outside.
I don't see something positive happening to an incel, so you would most likely fail sooner or later and just revert to your old self.
consider that research says that for something to become "normal" you need to do it at least 3 months.
that said I think there is no doubt that the way you perceive the world has an influence on your hormones, so feel free to try, but don't expect too much.