Initially, if one questions whether the personality can change, the most expected response would be no, or at least, not to a large extent, and this is due, in part, to the fact that we all know many people, and that very few people change in a very significant way, their way of being.
For example, do you know people who, being restless, active, and sociable, become calm and silent? Or someone who, from being suspicious and suspicious, becomes very open, altruistic or compassionate?, or even individuals who, being responsible, ordered and careful, then become impulsive people who enjoy improvisation in their way of doing things?
The truth is that there are few cases, of this type of changes and more if we exclude those that may be caused, for example, by a disease, such as depression.
Certainly who suffers from a relevant emotional disturbance, such as a depressive episode, it greatly modifies their habitual way of thinking, feeling and acting. Someone can go from being extroverted and active to being taciturn, lonely, apathetic and inactive. But that remarkable variation of personality is caused by an external factor, in this case depression. And for that reason it is only a transitory change.
As the mood of the individual improves over time or with a treatment, progressively its temperament and habitual character, will resurface until recovering the original configuration without leaving an observable trace of that depressive phase, as long as the recovery be complete.