I'm not sure about using Nix (the package manager) on other distros/macos, but I remember that when I tried out NixOS years ago, one of the things that struct me was just how little PATH stuff was needed. Literally the only thing in /usr/bin was `env`, and everything else was specific to each given package. My naive expectation would be that most of the stuff to be self-contained, like maybe a single script to `source` per package that could get set up as part of an invocation at the end of a shell config, and that worst case, switching back would be as simple as removing that invocation.