anchor.diff:        perl = "${pkgs.perl}/bin/perl -I${pkgs.perlPackages.FileSlurp}/lib/perl5/site_perl";
     } else throw "\nFailed assertions:\n${concatStringsSep "\n" (map (x: "- ${x}") failed)}");
   
  +  # Replace runtime dependencies
  +  system = fold ({ oldDependency, newDependency }: drv:
  +      pkgs.replaceDependency { inherit oldDependency newDependency drv; }
  +    ) baseSystem config.system.replaceRuntimeDependencies;
   
   in
   
  
positive.code:   # kernel, systemd units, init scripts, etc.) as well as a script
    # `switch-to-configuration' that activates the configuration and
    # makes it bootable.
    system = showWarnings (
      if [] == failed then pkgs.stdenv.mkDerivation {
        name = "nixos-${config.system.nixosVersion}";
        preferLocalBuild = true;
  
negative.code:       '';
      };
  
      system.replaceRuntimeDependencies = mkOption {
        default = [];
        example = lib.literalExample "[ ({ original = pkgs.openssl; replacement = pkgs.callPackage /path/to/openssl { ... }; }) ]";
        type = types.listOf (types.submodule (
          { options, ... }: {
            options.original = mkOption {
              type = types.package;
              description = "The original package to override.";
            };
  
            options.replacement = mkOption {
              type = types.package;
              description = "The replacement package.";
            };
          })
        );
        apply = map ({ original, replacement, ... }: {
          oldDependency = original;
          newDependency = replacement;
        });
        description = ''
          List of packages to override without doing a full rebuild.
          The original derivation and replacement derivation must have the same
          name length, and ideally should have close-to-identical directory layout.
        '';
      };
  
    };
  
  
  