I see it as the person that is left when people are stripped of their possessions, dignity, feelings of self-importance and self-confidence - basically, your motivation. How you are then is what you are at core. If we are happy, we have money and security, it is very easy to do the "good human being act" or whatever you like to call it. But of course, this is just an extreme example but that is what I mean by "beneath".
I am fully aware that we are on the verge of semantics here but here goes anyway. I see that as a change of behavior, not a change in personality. Let's say I'm lazy to the core but because I live with a woman who expects me to do certain things at home in relation to chores or kids, I'll go with it cause I want her to love and appreciate me. If I don't do that, I put the love and my security to risk. So everything I need to do these things, I feel like I really wouldn't want to (as opposed to "yeah, sure!"), I do it because that's acceptable behavior. Or you find money on the sidewalk. You would like to keep it but maybe upbringing has put into your head the idea that it's wrong and it's a good deed to return it to the owner?
If the case is such that previously you would've kept the money or would have been lazy jackass but no you are definitely not that, you don't even think about keeping the bucks or staying on the couch, then I can admit your personality has changed. Naturally, if you've gotten rich meanwhile, it doesn't tell that much about your changed personality but instead of changed circumstances which is not a proof of personality change.
It depends what are your motivations. If you are working harder to get recognized or get wealthy, then it's the motivation that is driving you - not your change of personality. If you still find yourself working immensely hard when there's nothing to be gained from it, then you've changed your personality. Motives always trump the core personality - it's more about what happens when those motives run out. That's when you are seeing the core personality.
Artificial and far-fetched to this discussion. What if I lose my leg - isn't it fair to say I have become one-legged? Traumas and sicknesses are a completely different matter if we are talking about people being able to change personality.