The state pledges to and agrees with the holders of any bond issued by the district or other debt incurred by the district, and with those parties who may enter into contracts with the district, that the state will not limit or alter the rights vested in the district by this subchapter until such bonds or other debt, together with the interest on the bonds and other debt, are fully met and discharged and such contracts are fully performed on the part of the district, but nothing shall preclude such a limitation or alteration if adequate provision is made by law for the protection of the holders of such bonds or other debt or those entering into such contracts.