parallels: add package config option

allows overriding of package with newer versions

nixos/modules/virtualisation/parallels-guest.nix

@@ -3,9 +3,7 @@
 with lib;
 
 let
-
+  prl-tools = config.hardware.parallels.package;
-  prl-tools = config.boot.kernelPackages.prl-tools;
-
 in
 
 {
@@ -32,6 +30,16 @@ in
           disable this to manually mount shares.
         '';
       };
+
+      package = mkOption {
+        type = types.package;
+        default = config.boot.kernelPackages.prl-tools;
+        defaultText = "config.boot.kernelPackages.prl-tools";
+        example = literalExample "config.boot.kernelPackages.prl-tools";
+        description = ''
+          Defines which package to use for prl-tools. Override to change the version.
+        '';
+      };
     };
 
   };