That’s essentially what you do when you wipe your system and install another distro. If you have a separate home partition that stays intact through the process then it’s especially true.

Yes, but you are asking for a world of pain. Why would you want to do this?

curious, why would you want that? the packages are usually built by the distro maintainers for the distro, so if you switch from, say apt to dnf you’d have to take care of repackaging yourself.

Yes it probably is but there is really no sense in replacing all the packages