In addition to any rights otherwise lawfully conferred, the articles of incorporation of the corporation may confer upon the holders of any bonds, debentures or other debt obligations issued or to be issued by the corporation any one or more of the following powers and rights upon such terms and conditions as may be prescribed in the articles of incorporation:
Any such power or right shall not be diminished, as to bonds, debentures or other obligations then outstanding, except by an amendment of the articles of incorporation approved by the vote or written consent of the holders of a majority in principal amount thereof or such larger percentage as may be specified in the articles of incorporation.
N.C. Gen. Stat. § 55-7-21.1