I have recently discovered a theory about personality that suggests we have a core personality (similar to MBTI) that we received at birth, but that which is NOT necessarily evident or obvious in a person, except at infancy. The idea is that the core personality devises ways to wear a different persona and that it is, more or less, a partly unconscious endeavor. Now MBTI suggests to do so means to exert more energy than needed because we have one personality that is the only minimal-energy-viable personality. I believe this is partly true; I believe if a person exerts the initial inertia of energy needed to be another type that once done will require minimal energy to use at will, it becomes a preference without the person being aware unless isolated and made to reflect on their identity. The idea uses Jung's idea of archetypes in place of personality. I think this is a correct approach. And I think the only problem anyone will have with this is supposed evidence of others failing to change their personality and ending up reverting back to a state already familiar or losing their (sometimes temporarily) sanity. This can happen for two reasons: not putting forth the appropriate energy or having too many roadblocks put in their cognitive way for it to be a worthwhile endeavor (thus the retreat). But I will discuss this below.
But what I want to get at now then is what has been covertly attacking the idea of personality on this board - multiple personalities. It seems what we really have here is a conflict between a belief in one personality and a belief in multiple personalities. Jung remarked that to have no personality was, for the most part, an unhealthy state to be so susceptible to other personalities and removed from a defined self to interact with the world in. If we take this to be true, then what can we say about the inverse? If someone has all or many of the personalities at their disposal, then what better way to interact with the world? Of course, this assumes quite a lot of initial building-energy and growth on an individuals part, but are we doing ourselves justice by eliminating the possibility?
But back with the idea of a person changing a personality, let us consider first those that fail. We can look at the homeless guy on the street walking back and forth talking to himself or the seemingly-psychotic patient in a mental ward going back and forth between different identities and playing with them, perhaps in search of finding one that can be used to align everything and help them interact well with their environment, and we can assume that having more than one personality is dangerous, can leave someone to such confusion and indecision that they can not interact, that having more than one personality means to be fragmented. But I propose that those individuals are fragmented because they never reached a personality state that defended them from great stress or that satisfied their needs with the world; they are (temporarily) broken, and for perfect reasoning, like a neglected now-inoperable machine that never received its maintenance services, and I suggest that those who have successfully integrated multiple personalities to mold many, instead of one, personality mask, are quite healthy and quite reasonable in attacking the idea of MBTI.