The problem with package based distros (everything non-immutable) is, that a distro is very complex.
Even if you manage to "swap out" the package repositories, you usually still have a lot of remaining stuff in the background and many things tweaked by the maintainers. It's a huge mess.
In theory, you could absolutely do that, but to be honest, why bother? You already always should have a backup of all your personal data, so why not reinstall it cleanly?
Speaking of image based distros ("immutable"), the cool thing about most is that that you can easily swap out the underlying OS with just one command.
For example, you can always rebase from Fedora Silverblue to Kinoite to Bazzite to something with Hyprland and then back to vanilla Silverblue, without any traces.
So, for example, if the guy who makes your custom image on Github stops maintaining it, you can simply switch to something else in just seconds.
Maybe this is something relevant for you :)