Is there a way to maintain your changes across wordpress. Not just the themes, but also the central app itself, and plugins. With themes, I get it, you just make a child theme. But suppose I want to change some things in the admin section? Won’t the changes be overwritten by the next upgrade? How do I avoid that?
What changes? All you configurations should remain without changes
You shouldn’t be editing WordPress core files! That just doesn’t make any sense, what are you trying to achieve?