Ludicrous at best...
A 3rd party auditor is required to audit several items:
1. Conformance to the relevant standard, i.e. ISO, AS, TS (both in the documented systems and the non-documented activities)
2. Conformance to internal documentation/specifications, i.e. company policies and procedures, including customer specific requirements
3. Depending on the nature of the audit, conformance to statutory and regulatory requirements that may be applicable to the industry, material or oragnization.
For the organization to require the registrar to only audit to their specifications is bass-ackwards. The registrar oversees the organization's qms, and is not dictated to or by the requests of the organization.... Sounds like the cart trying to lead the horse.... and IF your registrar has VERBALLY agreed to this (more like a salesperson, not a voice of the registrar with any credibility), I would not be surprised that your auditor may (WILL NOT) not follow those guidelines.