Technicly yes but it’d be hard and would probably break a lot of stuff. If you need a diffrent package manager its better to just install a distro that comes with it.

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

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.

Well, technically ya could. Given some effort you could entirely replace it, but there’s usually no point. Take NixOS’ package manager as an example. You can drop it into any dsitro and use their repos, but anything you can find there you’d usually be able to find in your native repos.