(a) Provided that the Federal agency and the certifying authority agree in writing that the certifying authority may modify a grant of certification (with or without conditions), the certifying authority may modify only the agreed-upon portions of the certification. The certifying authority is not required to obtain the Federal agency's agreement on the language of the modification.

(b) The certifying authority shall not, through a modification pursuant to paragraph (a) of this section:

(1) Revoke a grant of certification (with or without conditions); or

(2) Change a grant of certification (with or without conditions) into a denial or waiver of certification.