I used Create Locator in ArcGIS Pro to create a zip code locator using the ZIP role. My field mapping is just the ZIP field. I built the locator successfully. A couple questions:
1. The input fields are fixed for all locators created with the Create Locator tool regardless of the role the locator is based on. If it is just zip code, you should be able to use the SingleLine input field. Is the purpose of using the geocode service at the REST endpoint for development purposes to verify results or will the geocode service be used in an application?
2. To limit the output fields returned by the locator, turn off the unwanted fields in the Locator Properties of the locator in ArcGIS Pro on the Output fields page of the dialog. Then overwrite the service using the modified locator.
3. It's not possible to remove or customize the localized names for the locators created with the Create Locator or Create Feature Locator tools that are published as services.