In fact you can´t change the Edition/Addenda and he can´t ask you to do so. It´s stated in the Foreword of the Code:
After Code revisions are approved by ASME, they may be used beginning with the date of issuance. Revisions, except for revisions to material specifications in Section II, Parts A and B, become mandatory six months after such date of issuance, except for boilers or pressure vessels contracted for prior to the end of the six-month period.
To make it absolutely clear please refer to Interpretation VIII-1-95-29
Subject: Section VIII, Divisions 1 and 2 (1992 Edition, 1993 Addenda); Foreword, Table W-3, Note No. 13, and Table I-220, Note No. 12
Date Issued: January 12, 1995
Question (2): What Edition and Addenda of the Code is to be recorded on the Manufacturer´s Data Report Forms?
Reply (2): The current mandated Edition and Addenda of the Code at the time of contract between the user and the manufacturer