installation

first, you must edit /etc/nixos/configuration.nix to include the following:

{
  config,
  pkgs,
  ...
}: {
  imports = [
    ...
  ];

  nix.settings.experimental-features = [
    "nix-command"
    "flakes"
  ];

  ...

  networking.hostname = "<hostname>";
}

then, run sudo nixos-rebuild switch once to apply those changes.

finally, run sudo nixos-rebuild switch --flake /home/grey/nixos#<hostname> to apply the flake.

now you have access to nh os switch ~/nixos, and shouldn't touch the global config ever again.