Yes. A valid Operational Authorisation is not required to complete the GVC to RPC-L1 conversion course.
You will need an Operational Authorisation again before you carry out operational flights in the Specific Category, and you will need an Operations Manual in order to apply for one. Getting your certificate sorted first is the sensible order to do it in.
If you would like us to review your Operations Manual before you reapply, we offer that as a separate service at £125 + VAT — email [email protected].