Add nix-pin-revision script.

nix/configuration/configuration.nix

@@ -1,9 +1,16 @@
 {
   config,
   lib,
+  pkgs,
   ...
 }:
 
+let
+  alias_nix_pin_revision = pkgs.writeShellScriptBin "nix-pin-revision" ''
+    # Usage: nix-pin-revision nixpkgs 'github:NixOS/nixpkgs/00c21e4c93d963c50d4c0c89bfa84ed6e0694df2'
+    exec nix flake lock --override-input "''${@}"
+  '';
+in
 {
   imports = [
     ./roles/2ship2harkinian
@@ -140,6 +147,10 @@
     };
     nix.settings.auto-optimise-store = !config.me.buildingPortable;
 
+    environment.systemPackages = [
+      alias_nix_pin_revision
+    ];
+
     environment.persistence."/persist" = lib.mkIf (config.me.mountPersistence) {
       hideMounts = true;
       directories = [