What 'exactly' changed in Adam when he sinned?
Whilst I am not ?exactly? sure, the gist of it follows:
Jesus and Adam were different incarnations of the same soul... the Christ. So too was Mary and Eve different incarnations of the same soul. Kindred spirits if you like. (Many spirits that incarnated at the same times as Adam, were also known as ?Adam? or the Adam soul-group. The Adam soul-group appeared simultaneously in five different continents as five different races, white, yellow, brown, red and the fifth died out? but I digress.)
When Adam (the Christ soul) was banished from Eden this was actually a blessing of sorts, since death and reincarnation draws ones attention away from desires of the flesh. Basically, there?s nothing like staring death in the face to make you appreciate the source of your life. The Christ then realized at this point, that he was to become saviour of the world. A karmic debt was owed to Eve (since Adam got into trouble), and this was repaid to Mary in his life as Jesus.
BTW, the forbidden fruit represented ?materiality? in general. There was no apple to speak of. There is a hint of this in Genesis when it speaks of interbreeding with the ?daughters of men?.
I don?t have all the answers, but I know I?ve only just scratched the surface here.