In the case of planned unit developments which are approved by the Commission and the Board of Trustees in accordance with Chapter 415: Zoning Regulations, the approved planned unit development shall be considered to be an approved sketch plan, and the subdivider may proceed to submit a preliminary and final plat, as necessary, in accordance with these Regulations. The Commission may grant such variances as are necessary in the preliminary and final plat to accomplish the purposes of the approved planned unit development.