Section 28-102.4.3. Alteration of existing structures

Except as otherwise
  provided in sections 28-101.4.1, 28-101.4.2, 28-101.4.3 and  28-101.4.4,
  existing  structures altered after the effective date of this code shall
  comply with the provisions of this code. In accordance with  subdivision
  eleven  of  section  three of the multiple dwelling law and article 4 of
  subchapter 1 of the 1968 building code, at  the  option  of  the  owner,
  multiple  dwellings erected prior to December 6, 1969 may be altered and
  buildings erected prior to December 6, 1969 may be converted to multiple
  dwellings in accordance  with  applicable  provisions  of  the  multiple
  dwelling  law  and  the building laws and regulations in effect prior to
  December 6, 1968, provided the general safety and public welfare are not
  thereby endangered.