In existing zones, the Planning Commission and City Council may proceed to rezone such zones to an equivalent planned commercial zone without the requirements of a preliminary development plat and other necessary information. After being so zoned to a planned commercial zone, a preliminary and final development plat of each development shall be submitted to and approved by the Planning Commission in accordance with the provisions of this chapter prior to the issuance of building permits; provided, however, that improvements already in existence at the time of rezoning shall not be affected. (PZSC § 03-25-012)