This is a popular question. In short, it’s highly unlikely.
It’s hard for anyone to make long-term changes in their life, but this disorder makes it beyond challenging. I’ve heard therapists and counselors say they simply will not work with a narcissist because the progression in recovery takes a lot of energy and is very minimal, if at all.
They would need to be committed to the long-term therapeutic process and the further up they are on the spectrum, the more difficult this can become because they are managing the disorder itself on a daily basis, which makes little room for growth and self-improvement.
So, while I believe it’s possible for them to change behaviors, I don’t believe it’s probable long-term.
We also need to consider, that they could simply be dealing with some narcissistic behaviors and not suffer from high traits or narcissistic personality disorder. They may be dealing with other disorders or addictions that are causing their behaviors. Sometimes when those are managed properly, the narcissistic behaviors decrease or can return to a normal range.
As I always mention when someone asks this question, there can be a huge change, but it has to come from you, not the narcissist.