The municipalities entering into a joint contract for the construction, maintenance and operation of any improvement or works authorized by section 40:63-70 of this title, may alter or modify any of the provisions thereof, and provide for the future maintenance and operation of the improvement or works by a supplemental contract, authorized by ordinance or resolution of each of the governing bodies or by the boards charged by law with the construction of sewers and drains in the several contracting municipalities.
N.J.S. § 40:63-83