Can a person be psychologically transformed?
I would like to establish a difference between the previous highly optimistic answer and in-depth psychological change.
Although it is true that the psychological community might agree that people can change, behavorists do not take into account the basic psychic structure but only its manifestations. Therefore, they sincerely believe that observable changes in appearance and manner reflect changes in the structure.
I'm afraid that Lacan's teachings, not very popular with the American "psy" community, show another reality. An individual's psychological structure is immutable. What can change is what the individual does about and with her structure. Thus, what changes (through introspection, meditation, psychotherapy, psychoanalysis, you name it) is an individual's attitude to herself and to her environment, while her psychological structure will remain the same. Therefore it may not be a good idea to speak of psychological transformation, but of making the most of a given structure.
This is a great question. There will many different opinions. For example, in the ancient Greek and Roman world, people believed that no one could change. They believed that you could hide things for a while, but the true personality of the person would eventually come out.
In more modern times, most people believe that people can change, even if this change is difficult.
First, if you talk to any religious person, they will say that change is possible. In fact, all of Christianity is based on the assumption that people's minds can be transformed. This is what religious people call a conversion.
Second, if you talk to a community of psychologist, they, too, will say that people can change. What makes this point more cogent is that different schools of psychology will say the same thing, namely that people can change.
Finally, if you take a more anecdotal approach, people will say that they have experienced transformation and seen this in others as well.