You can create or remove parameters for use in your custom IP. When adding parameters, you can only add parameters for use in the Customization GUI. To add a parameter to reference the top-level HDL, the source files must be modified and the parameters must be re-imported.
You can remove any parameter from the list regardless if it is referenced from the top-level HDL. If an HDL parameter is removed from the Customization Parameters list, a default value is required in your top-level HDL source.