1. Maybe. Over the course of my life, it seems that Ne and Fi have traded places a few times. My Fi was surely the first to develop, I was a classic IxFP child, but Ne developed way earlier than the auxiliary is supposed to develop (probably around second grade). In mid to late elementary school, I became quite Ne-heavy, but Fi was never abandoned; I have always been a feeler above all else. In seventh grade, I went through a rebellious, intentionally defiant, self-described communist (didn't even fully understand the concept at twelve) phase that could've been interpreted as very ENFP-ish. Was clearly introverted and Fi dominant for eighth and ninth grades, but I met some good friends, and my Ne exploded. Maybe that's the aux development they talk of.
But no, I don't think I've changed. Just fluctuated and developed.
2. Not sure. I was actually very, very 9w1-ish as a young child, with a 2 fix. Sometime in third grade, I started feeling that "fundamentally different" 4 thing, and felt deeply upset to have been born abnormal (which I was, and I still consider myself to be happily out-of-sync with others), but some of that is honestly just angst that everyone goes through. 6 fix seemed apparent for a long time, fluctuated between phobic and counterphobic. 6w7 and 9w1 have always been very prevalent. Heart fix seemed to be a fluid 2w3/4w3 thing, but I'm convinced that the 4 was just a product of Fi, 6w7, my mental health issues, bullying, and normal angst.
So I've always been 2w3, 9w1, and 6w7 of some sort. Order of fixes probably changed.