Design changes to any publicly accessible open area, required open area or indoor public space previously improved pursuant to the provisions of Sections 91-832 (Plaza improvements) or 91-834 (Indoor public spaces) may only be made upon certification by the Chairperson of the City Planning Commission that such changes would result in a publicly accessible open area or indoor public space that is compliant with the Section under which it was previously approved. As part of the certification, a horizontal enlargement on the ground floor level may be permitted along existing building walls that face the publicly accessible open area and do not face an arcade, but such enlargement shall not occupy any publicly accessible open area. The locational requirements of paragraph (a)(1) of Section 91-831 (Ground floor requirements) and the use and transparency requirements of Section 91-831 for new building walls facing a publicly accessible open area shall apply. The legal requirements of paragraph (a) of Section 91-836 shall apply.