I've read that the only "cure" for true personality disorders is to fake it until faking it becomes second nature. For example, narcissists pretend to care about the needs of others until they sort of start to automatically care about them.

Yes, this is the "fake it 'til you make it" idea. It is controversial though, because there's an enduring implication that, e.g. the narcissist does not really care about others, they're just pretending to do so.