People presumably change some. If nothing else, we all get older. But I'm not so sure about unlearning something. If anything, I think we learn new things that get overlaid on top of what we already know. I'm not referring to habits, however, which you may be. I don't know that you ever lose your roots. But if you mean by cutting down the tree, you get back to your roots, then you may be on to something. You might grow a little differently in different soil, in a manner of speaking. But just like a tree, you're either growing or dying. Nothing is going to stay the same.
Reunions, if anything, are where you expect to see old friends, not to make new ones. To renew old acquaintances and to catch up with the news of the past decades. In my case, I moved away and so I'm the one who has to go back, even to see such family as I have left back home.