Any proposed amendment to this chapter must be adopted by a vote of the Board of Commissioners of at least two-thirds of the votes then eligible to be cast. Upon approval by the Board of Commissioners, the amendment shall be submitted to the legislative bodies of the respective member municipalities. A majority of the legislative bodies of the member municipalities must likewise approve any proposed amendment. Upon such approvals, the amendment shall be submitted and acted on by the General Assembly in accordance with the provisions of 17 V.S.A. § 2645. The amendment shall become effective upon affirmative enactment of the proposal, either as proposed or as amended by the General Assembly. For the purposes of this section, this chapter shall be considered a municipal charter.