Subject to the provisions of the declaration, section 4321(c) (relating to limited equity cooperatives) and other provisions of law, a proprietary lessee:
(1) May make any improvements or alterations to his unit that do not impair the structural integrity or mechanical systems or lessen support of any portion of the cooperative.
(2) May not change the common elements or the exterior appearance of a unit without permission of the association.
(3) After acquiring a cooperative interest of which an adjoining unit or an adjoining part of an adjoining unit is a part, may remove or alter any intervening partition or create apertures therein, even if the partition in whole or in part is a common element, if those acts do not impair the structural integrity or mechanical systems or lessen the support of any portion of the cooperative. Removal of partitions or creation of apertures under this paragraph is not an alteration of boundaries.