The board may provide in the resolution authorizing the issue of any bonds under this chapter the terms and conditions upon which any provision of any resolution of the board constituting a part of the proceedings for the issuance of such bonds, or any provision of such bonds or coupons appurtenant thereto, may be modified if consented to by the holders of any percentage, specified in such resolution authorizing the issue of such bonds, of the aggregate principal amount of the outstanding bonds of such issue.