These questions may be kinda vague, but I hope someone well versed in typology can give me some answers. Can a very difficult and stressful childhood coupled with a response of emotional suppression and any other number of environmental and internal factors actually mold one into a different type (such as a thinker instead of a feeler, or I instead of E)?
Just a few quick thoughts on this:
1. We are not really "MBTI types," we simply are born with function preferences.
2. The functions we get good at are based on preference; we do them more often, we become skilled.
3. Healthy environments give us freedom to develop our natural preferences; unhealthy environments force us to learn coping mechanisms that are not our natural bent.
4. The more extreme that disparity is (i.e., the more we have to suppress natural inclination), the larger the internal conflict between who we are naturally and who we are being forced to be. This causes a lot of problems in life.
In a healthy setting, we do not feel guilt over developing our innate preferences; and we also are stretched just enough to develop an appreciation with other preferences ... and perhaps even develop those some by our own choice. It's when the other preferences are imposed over the natural ones that disruption occurs and then a host of other emotions interfere (such as frustration, anger, shame, disappointment, self-loathing, etc.)
If so, does that mean that what we were before is still our most "natural" way of functioning, our true type, or are we forever changed? This is assuming that we start out very very early in life with a definite type preference. I guess I'm wondering, if one is forced to carry extreme burdens in the stage of life when we are rapidly developing our personalities and developing our sense of self, how much of an effect can that have on transforming our personalities, and is there any going back?
If you think about it as far as playing the piano, for example -- you might have had an innate skill at doing it (i.e., it might have come easier to you than others) and you would have WANTED to do it but didn't. So yes, you still have that innate ability and desire/preference; but you'd still need to give yourself opportunity to practice and develop the skill to get good at it. And that development could be influenced (strengthened/diminished) by who you have become in the meanwhile.
Basically, the goal is "find your more natural self" and accept it and let it flower. Meanwhile, preserve what you can of the rest and use it to your advantage. I think that allows for the most development of personal potential.
You also want to avoid "defining" yourself up front. Listen to what's inside. Go with it, while keeping a perspective on where it might lead you so you can separate mere preference from selfishness.
Also avoid doing things just to control what others think of you. (For example, Thinkers sometimes hate showing emotion because then they feel the people around them might think they're emotional and stupid, rather than smart and thought-oriented. Don't let the "Thinker" aspect control your expressiveness; accept that you can be a good thinker at core and still show emotion to the people you care about. When we do that, we're not acting naturally; we're trying to manipulate public opinion so people can perceive us how we want them to.)