Tenn. Code Ann. § 7-60-212

The state does hereby pledge to and agree with the holders of any bonds or notes issued pursuant to this chapter that the state will not limit or alter the rights vested by this chapter in a county to fulfill the terms of any agreements made with the holders of the bonds or notes, or in any way impair the rights and remedies of such holders until such bonds and notes, together with the interest on the bonds and notes, 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 such holders, are fully met and discharged. A county is authorized to include this pledge and agreement of the state in any agreement with the holders of bonds or notes.