Answer
No. When you create a geocoding service against a feature data object data source, the geocoding service creates a geocoding index on the fields in the reference data source that contain the address information. If you were to change the fields in the reference data source that the geocoding service used, the geocoding index would no longer work for your geocoding service. To create a geocoding service that uses different fields from the reference data source you need to create a new geocoding service.