The state pledges and agrees with the holders of bonds issued under section 37.31 that the state will not limit or alter the rights vested in the society to fulfill the terms of any agreements made with the bondholders or in any way impair the rights and remedies of the holders until the bonds, together with interest on them, with interest on any unpaid installments of interest, and all costs and expenses in connection with any action or proceeding by or on behalf of the bondholders, are fully met and discharged. The society may include this pledge and agreement of the state in any agreement with the holders of bonds issued under section 37.31.