Most people will believe whatever you tell them your MBTI type is. Some variation of Forer effect, I suppose.
In my own experience, I consider the notion of type "changing" to be irrelevant. Given how MBTI isn't anything near an exact science, one can never know with absolute certainty what their type without disregarding information that disagrees with their position. In addition, confirmation bias occurs much more easily and more commonly in individuals that hold they are a certain MBTI type.
My personal response to this problem is weigh the likelihood of being any one type over another based on the data provided without committing to any single option. Presently, based on my data, INTP seems like my most likely type. New input to my model does not disprove the model. Rather, it allows for an expansion of the model due to the new chunk of data that can be incorporated. Even if I appear to be more ISTP-ish than in a previous timeframe, it is fully possible that I have been ignoring something for whatever reason.
In other words, adjust your type according to what you know. Whether this adjustment was merely "correcting" a mistyping or indicating a change in your type does not matter. At this point in the development MBTI theory, there is no way to know which of the above scenarios prevails. However, even without knowing, one can "change" their opinion on their MBTI type without knowing what caused it.
If a deaf INFP falls in the forest and no one is around to hear it, does it make a sound?
What is genetic? It would be hard to prove that some attribute of mind is strictly genetic. That leads to a sort of biological determinism with the end result being ascribing certain personalities to various races, genders, etc.
Well, we all know that females are physiologically different than males. Thus, they are also psychologically different from males because the brain is a physiological construct.
Hormonal levels and other biological catalysts are determined by physiological means. We also know that they can cause drastic changes in behavior and "personality".
However, the human body is a very adaptable and malleable tool. It often changes to cope with imposing environments. So, it is feasible that the mind and personality are adaptable as well.
But I'm sure you already know this. I'm just typing incessantly to sound quasi-intelligent.
I think people can change type for a time, maybe a certain time of their lives. But soon enough, they will revert back to the type that they were born with. I think that deep, down, we will never change
I believe you can switch your function though, but not your whole type. ex. using feeling when stressed for the not so feeling type people. So to others it may seem your being different than who you normally are.
I subscribe to the assumption that you will always have a preferred type, and thus a preferred function makeup. I think a lot of people don't realise that the theory says you don't have a good grasp of those four functions straight away, and that you develop them over time as you mature and start accepting parts of you (and ways of seeing the world) that you once tried to fight (for example, I'm convinced that we tend to demonize our inferior function when we're very young, and we can easily make excuses to not use the auxillary function when we need to deal with something that is outside the capabilities of the tertiary function).
There's also nothing stopping you from developing your ability to handle the four other functions as well (for example, we are all subjected to extraverted thinking on a daily basis), so that could give the illusion of you changing your type. But I do think there's always a preferred function order that "feels" the most like you.