All preliminary plans, final plans, revised preliminary or final plans and all development plans of any type which have been approved by the Mayor and Common Council and/or the Commission prior to November 5, 1979, shall continue to be approved and valid after said date, regardless of the zonal classification of the real property as to which such plans pertain, and said real property shall be developed in accordance with the provisions of such plans. Such plans may be amended in accordance with the procedures provided for the amendment of development plans contained in § 164-188J of this chapter. Additionally, the Common Council may amend any such plans approved prior to November 5, 1979, to permit residential single-family attached dwellings in lieu of any commercial or business use, provided that it determines, after an opportunity for public comment, that there will be no increase in the gross allowable residential density beyond that originally approved and that such development will not have an adverse impact upon the adjacent properties or the general character of the approved development plan.