There are two areas of human behavior and thought process that cannot be changed: First there are the biological imperatives that cause us to react in ways that are instinctual, physiological or mysteriously, just there as a fixed part of us. Second, there are physical or illness issues that can permanently change or fix behavior in ways that cannot be undone.
As for anything else, it seems that anything goes. People have changed a host of processes that were imposed upon them or that developed during their upbringings and experiences in life. Humans have been led into cults. There have been intense religious, military or spiritual journeys. A person who has become devoted to practicing science or the arts has practiced and incorporated all forms of unusual and different behaviors and actions, again and again, until they became a part of the person's makeup.
Shy people have turned out to be outgoing and highly confident entertainers, performers, social animals and public speakers. Outgoing attention seekers have become comfortable in their own skins and stopped trying to draw attention to themselves. Shopaholics have become frugal. Obsessed fans have burned out on their favorite celebrities.
Some processes of change are actually a freeing up and rejection of the values, norms and beliefs that are imposed in childhood. These may be rejected when a young person enters the world and lets go of that which was traumatic, trying or undesirable.
Other processes of change are products of assisted change programs, such as psychological or spiritual counseling, for people who are in conflict, are ordered by the courts, or undergo rehabilitation after addiction, trauma, major illness or injury.
The world introduces incentives to change. Living a different country involves a whole world of change; in speech, behavior, norms, etiquette, and other areas that are essential to fitting in. A change in financial, professional or social standing can result in a lot of change in human conduct that is tied to those factors in life. A poor person who wins a lottery might change into a more discriminating and savvy person who expects quality in service, support and material things. A wealthy person who loses their fortune might change into a frugal and savvy survivor who can live quite happily with less. Losing a physical capacity involves a whole change of expectations and conduct in life.
A person who had never lived in a war zone will probably change their ideas about behaving aggressively in self defense. A person who has always lived in war zones will have to change their ideas about behaving aggressively when they move to areas that do not require a constant focus on self defense.
Humans, if they do not have a fixed and permanent physiological issue or a medical problem that will never allow them to change, are capable of making incredible changes to any part of their faith, belief, norms, values, judgments, standards and behaviors. Sometimes this requires help and hard work over time. Sometimes this is a reaction to changes and threats from the world around us. Sometimes change is the consequence of a passion or vocation in life.