If a district desires to extend the time or times of maturity of any or all of its bonds or warrants payable at stated times or to reduce the rate of interest thereon or to effect any combination of these, it may either:
(a) Enter into an agreement in writing with the holders of the bonds or warrants affected, specifying the changes in dates of maturity, rate or rates of interest, or both.
(b) Propose a plan of composition of its outstanding indebtedness which involves changes in dates of maturity, rate or rates of interest, or both.