Subsequent amendments to Sections 37-145-43 through 37-145-73 shall not limit the rights vested in the company with respect to any agreements made with, or remedies available to, the holders of bonds issued under Sections 37-145-43 through 37-145-73 prior to the enactment of the amendments until the bonds, together with all interest thereon, and all costs and expenses in connection with any proceeding by or on behalf of the holders, are fully met and discharged.