A bit of an extra tidbit of information, that’s why things like /usr/local exists: to keep things separate from the distro provided packages. A lot of things have directories in /etc for the sole purpose of isolating “what the distro provides” vs “what the user provides”. Often you can mask distro-provided settings by symlinking the same in /etc to /dev/null.
So it’s best to assume /usr is managed by your package manager and you shouldn’t touch it because it’ll be overwritten on next update. Or in the case of immutable distros, you can’t even write there yourself.
Plus when you do backups and restores, you can backup /etc, reinstall your distro, then restore your /etc and you should mostly end up back where you were.