I still have the personality trait of being an introvert, but when I was specifically working to push myself, my tolerance for "things" was increased. So while my personality hasn't changed, specifically my preferences haven't changed, my tolerances and ability to enjoy things outside of my preferences has been flexible.
I wonder if that's what a lot of these self-reported people reported. "Before I couldn't go to a party and enjoy myself, now I can!" isn't exactly indication that their personality changed. Even if they enjoy the parties and want more, I'd argue that their personality could still be the same - it has been for me.
I also think ultimately my self-identified trait of introvert might not be correct - and likewise many subjects here I wonder if they might be incorrectly self-identified. For myself, what I think I really dislike is not the outside/etc - it's new encounters. I hate them. Really, I loathe them. Even things as simple as driving new places. The unknown area, the frenzied feeling of finding the correct street, parking in cities, etc. I don't like driving because of that, honestly. So am I really an introvert? I actually like going places, it's just that life brings a lot of unknowns, and those are ultimately what I dislike and I have to fight to keep a reasonable hold on.