Section 27-118. Alterations involving change in occupancy or use

(a) Except
  as otherwise provided for in  this  section,  if  the  alteration  of  a
  building  or  space  therein  results in a change in the occupancy group
  classification of the building under the provisions of subchapter three,
  then the entire building shall be made to comply with  the  requirements
  of this code.
    (b)  Except  as  otherwise  provided  for  in  this  section,  if  the
  alteration of a space in a building involves a change in  the  occupancy
  or use thereof, the alteration work involved in the change shall, except
  as provided for in this section, be made to comply with the requirements
  of  this code and the remaining portion of the building shall be altered
  to such an extent as may be necessary to protect the safety and  welfare
  of the occupants.
    (c)  When,  however, the cost of alterations involved in the change of
  occupancy of an existing  building  erected  prior  to  December  sixth,
  nineteen hundred sixty-eight or space therein authorizes the alterations
  to  be  made in compliance with the applicable laws in existence on such
  sixth day of December, nineteen  hundred  sixty-eight,  such  change  in
  occupancy  may  similarly  be  made  in compliance with such prior laws,
  provided  the  general  safety  and  public  welfare  are  not   thereby
  endangered,  and  further provided that the alteration work shall effect
  compliance with all requirements  of  this  code  relating  to  interior
  finish  work,  finish  flooring and floor covering, sprinklers, interior
  fire alarms, fire command and communication  systems,  elevators,  smoke
  detectors, directional signs, emergency lighting and emergency power.