In addition to the powers authorized in Sections 3-21-2, 3-21-3 and 3-21-4 N.M. Stat. Ann., any county and any municipality may agree to authorize a joint municipal-county zoning authority to enact ordinances, regulations, or both, relating to approval and regulation of subdivisions within the extraterritorial zoning area as defined by the agreement creating the joint municipal-county zoning authority. Such subdivision ordinances and regulations shall be adopted, amended and enforced pursuant to Sections 3-21-3 and 3-21-4 N.M. Stat. Ann., as appropriate. Such subdivision ordinances and regulations may define “subdivision” in a manner which differs from the definitions set forth in Subsection A of Section 3-20-1 N.M. Stat. Ann. and in Subsection I of section 47-6-2 N.M. Stat. Ann.. The joint municipal-county zoning authority may also modify portions of the comprehensive plan, provided that such modifications leave unchanged those portions in the comprehensive plan that are not in the extraterritorial area.