so in a way you believe in the "blank slate" theory meaning that a mind is a blank slate that can be filled in by experience? do you believe anything is pre-defined?
i still stand true to the nurture vs nature arguement. i grew up with two INXJ parents and came out an ENFP. I know another ENFP that grew up with two SJ parents. i highly doubt that MBTI is developed purely on the basis of purely nurture. as far as drugs/trama/emotional/physical blah blah blah go, i dont think the type changes but mearly distorts. to me, the types are set in stone but are able to flex and sway in different directions based on environment and upbringing. a stupid analogy would be a building whose foundation is set but is allowed to flex with any earthquakes that it might encounter through its life.
the enneagram seems to be very easily changed by upringing/nurture/environment
EDIT:
the personality is defined by certain chemicals at a neuro-cognitive level
EDIT2:
blank slate argument: if a persons mind is effected by (completely by) environment then the mind must, to some extent be a blank slate. so if you take a baby and put him/her in a white square room with nothing it it and they do not need food/water/watever, then once older, will their mind be void? of course not, there are certain "instincts" or cognitive predispositions that we are born with. this has been proven by a very simple test. you take a new born baby and you show them two pieces of paper. one piece of paper has two equal sized dots above a smaller dot (eyes and a mouth). the other paper has one dot with two dots below it (? lol). the baby will always look towards the first paper. other tests have been done like this but that is just an example. so if they are born with the "instinct" to know what a face is then why cant they be born with a tendency towards a certain type? (people who are blind and deaf have personalties and yet there is almost zero input on their part) it is amazing how much babies learn in the first two years considering they are predisposed to knowing it