There have been times when I have thought that I have changed quite a lot over the years. But then sometimes I think that maybe I haven't....but that speaks more to what you say about core aspects remaining unchanged.
I'll provide one concrete example, which a friend has commented on, and then I'll go off on my own ramblings.

I met this friend about 8 yrs ago, and lived with her a few yrs back then. Quite recently we went on a trip together, and she told me that she thinks I'm the one friend she has who has really changed, and 'blossomed'. Related to the trip, she made a comparison between now and 8 yrs ago. She asked if I remembered how 8 yrs ago when we went to an outdoor concert, on the way back to the car I was very cautious, nervous about entering an alley, just in general a lot of trepidation in my approach to the world. And how now, I'm traveling around the world by myself, and I'm the one convincing HER to do things on the trip, or try things out, and she tells her friends about me. When she told me this, I was like....huh.....

The constant within my persona, that many people comment on, is that I am 'Thoughtful' and I put a lot of thought into pretty much everything I do. I'm just always contemplating and thinking about stuff. I typically have a reason(s) behind doing things, or choosing one thing over another - from the little to the very big. I think I've always been this way.
So my internal traits probably haven't changed a whole lot, but my perceptions about things have morphed quite a lot over the years. And perceptions are what drive behaviors and approach to the world and others - at least for me. So my change in perceptions have impacted my external behaviors - in social settings, in making decisions about my life and what I want out of it, etc.
A quick summary of behavioral changes -- as a teenager I was quite closed-off from all of my peers, and didn't really have any friends, or allow myself to get close to others. For one I don't think I knew how to, but also I had a rather intense Fear of people. I was scared of people, and what people did. I got this fear primarily out of observing people, because observation is pretty much all I did in school. Observation and going off into my thoughts. And in addition, internalizing teasing directed towards me, which made me not trust anyone. I was also quite lonely though, and unhappy that I didn't have any friends. Like, I felt I had it in me to have friends, and my state disgusted me, but it wasn't in me at that time to change it, due to the fear aspect, and insecurity on my part. In college I made the executive decision to try to do everything opposite how I was in high school, since I'd been relatively miserable in high school. So I started afresh, no past following me, no one knew me, and I ended up having several friends and having quite a different existance than I'd had as a teenager. I could go further into this, and add that I was denying/hiding many pieces of myself while doing this, but suffice it to say I had fun, I wouldn't do it much differently if I were to go back, and by the end of college I was starting to spontaneously shift back a bit more to how I was as a teenager -- but with added elements of more confidence and less fear. I do feel it appropriate to add here though that in my journal from my sr. year in college, I wrote that I took a 300 question personality test and I didn't like the results, which told me at that time that I had low agreeableness, low altruism, low friendliness, low sympathy, and low trust, and that "I have to start working on this!!" This is interesting to me because as I've written before, it really begs the question on whether Type can or cannot change -- because I was no NF (at least externally) back then.
My 20's have also had a large internal component to them. I've done a lot, and tried to push my boundaries a lot. In my early 20's I was still pretty closed off to my own emotions, and for a few yrs in my mid-20's I explored all of them, and since then have incorporated them as an important part of my life and my personality (but prior to that?? They were buried quite deeply and were probably pretty repressed). And finally, it's only in recent years that I think I've really become more open to others and am finally starting to feel solid about my own identity. Also there's been a bit of a shift from a more pessimistic outlook on life to a more optimistic one. And this in turn impacts how I approach others, and the nature of my relationships.