There are many researches to support the idea of change.

A recent study published in the Journal of Personality and Social Psychology said that narcissism can decrease with the age.

I studied

Dr. Craig Malkin’s book Rethinking Narcissism: The Bad — And Surprising Good — About Feeling Special, and he says A narcissist can change but "if" he wants.

According to him the change requires a deep emotional and therapy work.

I am mentioning my article , Once a narcissist, always a narcissist? just for further readings

https://medium.com/illumination/can-narcissists-change-5aee0aefa515