(a) After the adoption of the comprehensive master zoning plan, the Capitol Zoning District Commission shall have exclusive authority over the zoning and regulation of the utilization of all property within the Capitol Zoning District, and no planning or zoning authority or jurisdiction of any subdivision of the state shall have any zoning or control authority except as agreed upon by the commission.

(b)

(1) After the adoption by the commission of the comprehensive master zoning plan, the commission shall have the authority to approve or disapprove the location and design of any improvements to be placed upon any land within the district, and no improvements shall be placed upon any land within the district unless the design and proposed location shall be approved by the commission.

(2) Such improvements shall include, but not be limited to, buildings, including additions and alterations, parking lots and facilities, and all other construction whatsoever, except that the word "improvements" shall not include existing streets, alleys, or utilities and shall not include maintenance, service, or improvement thereof.

(c) After the adoption by the commission of the comprehensive master zoning plan, no improvement of any nature nor any change of land use shall commence within the district without a permit issued by the commission.

(d) Within the district, a legally existing use, building, or structure that exists at the time of the adoption of the plans and regulations authorized by this subchapter, but not in conformity with such plans and regulations, may be continued but shall not be extended or structurally altered without the approval of the commission.