§ 20.29. Agreement of the state. The state does hereby pledge to and agree with the holders of any bonds or notes of a trust that the state will not limit or alter the rights vested in a trust by this article or by special law to fulfill the terms of any agreements made with the holders thereof, or in any way impair the rights and remedies of such holders until such bonds or notes together with the interest thereon, with interest on any unpaid installments of interest, and all costs and expenses in connection with any action or proceedings by or on behalf of such holders, are fully met and discharged. A trust is authorized to include this pledge and agreement of the state in any agreement with the holders of such bonds or notes.