NixOS + overriding

Let's customize one of the installed packages in the system (vlc);

{ config, pkgs, callPackage, ... }:

{
  imports =  [ ./hardware-configuration.nix ];

  boot.loader.systemd-boot.enable = true;
  boot.loader.efi.canTouchEfiVariables = true;

  services.xserver.enable = true;
  services.xserver.displayManager.gdm.enable = true;
  services.xserver.desktopManager.gnome.enable = true;

  users.users.alice = {
    isNormalUser = true;
    extraGroups = [ "wheel" ];
    packages = with pkgs; 
      let 
        customFFMpeg = callPackage ./build_my_ffmpeg.nix {};
    [
      firefox
      (vlc.override { ffmpeg_4 = customFFMpeg; })
    ];
  };

  system.stateVersion = "23.11";
}

Benefit: custom system components + up to date versions.