Developments or enlargements within the Perimeter Area shall be eligible for increased floor area only pursuant to Sections 96-21 (Special Regulations for 42nd Street Perimeter Area) or 96-22 (Special Regulations for Eighth Avenue Perimeter Area). Because of increased pressures for development, the relocation and demolition provisions of Section 96-24 (Relocation and Demolition of Buildings in the Perimeter Area) shall apply therein for all demolition, development, enlargement or extensions on lots containing residential uses. All existing legal uses in enclosed buildings shall be considered conforming uses. Except as otherwise provided in this Chapter, any existing commercial or manufacturing uses may be changed to another non-conforming use only in accordance with the provisions of Sections 52-31 (General Provisions), 52-33 (Manufacturing or Related Uses in Residence Districts), 52-34 (Commercial Uses in Residence Districts), 52-35 (Manufacturing or Related Uses in Commercial Districts) and 52-36 (Non-conforming Commercial Uses in Commercial Districts).