Co-location on communications towers, structures or land encumbered by an antenna, structure or communications tower existing prior to July 2018. Notwithstanding anything to the contrary herein, the co-location requirements of this article are intended to be enforceable as to existing antennas, communications towers and structures and/or land encumbered by antennas, structures or communications towers. Accordingly, upon a renewal, extension or exercise of option for a renewal term of an existing lease for land, structure or communications tower, a clause in any such lease, whether entered into prior to or after the enactment of this article, which provides for exclusivity as to the land, structure or communications tower in favor of one or more carriers, shall not be enforceable against a carrier seeking co-location.