Wish: easier upgrading

Version upgrades could be made easier by separating the stuff that needs to be upgraded from that that does not.

It’s not difficult per se, but having “overwrite this but don’t overwrite that” files in “delete that directory except for that subdirectory” makes it rather tedious and error-prone. Wouldn’t it be nice to be able to just copy over one subdirectory tree and be done with it? (except for major changes and database upgrades, of course)