os/doc/concepts/overrides.md

Overrides

Each NixOS host follows one channel. But many times it is useful to get packages or modules from different channels.

Packages

You can make use of overlays/overrides.nix to override specific packages in the default channel to be pulled from other channels. That file is simply an example of how any overlay can get channels as their first argument.

You can add overlays to any channel to override packages from other channels.

Pulling the manix package from the latest channel:

channels: final: prev: {
  __dontExport = true;
  inherit (pkgs.latest) manix;
}

It is recommended to set the __dontExport property for override specific overlays. overlays/overrides.nix is the best place to consolidate all package overrides and the property is already set for you.

Modules

You can also pull modules from other channels. All modules have access to the modulesPath for each channel as <channelName>ModulesPath. And you can use disabledModules to remove modules from the current channel.

To pull zsh module from the latest channel this code can be placed in any module, whether its your host file, a profile, or a module in ./modules etc:

{ latestModulesPath }:
{
  imports = [ "${latestModulesPath}/programs/zsh/zsh.nix" ];
  disabledModules = [ "programs/zsh/zsh.nix" ];
}

Note:

Sometimes a modules name will change from one branch to another.