N.M. Admin. Code § 10.8.2.18
If a licensee wishes to add another category or additional higher calibers of handguns to his or her license, the licensee shall file with the department an endorsement application. The licensee shall also submit a certified copy of a certificate of completion from an approved instructor stating that the licensee has demonstrated competency on a firing range for each additional category and caliber of handgun, his or her current license, and a $10 processing fee. The licensee need not retake the classroom portion of the firearms training course. The department shall issue an updated license within 10 days of receipt of the application. The updated license shall expire on the same date as the original license would have expired. In accordance with Section 29-19-9 NMSA 1978, a licensee shall not carry the higher caliber concealed handgun until he or she receives the updated license
N.M. Admin. Code § 10.8.2.18