§ 12. Amendments to certificate of incorporation. The certificate of incorporation of any cooperative corporation may be amended as approved by the affirmative vote of two-thirds of the members voting thereon at any regular or special meeting, or, if the corporation permits its members to vote on the basis of patronage, by the affirmative vote of a majority of the members and of two-thirds of the patronage, voting thereon, provided that the certificate as amended be authorized by the provisions of this chapter applicable to such corporation. A written or printed notice of the proposed amendment and of the time and place of the meeting to vote thereon shall be delivered to each member, or mailed to his last known address as shown by the books of the corporation, or published in a periodical issued by the corporation and mailed to all members, at least twenty days prior to any such meeting. If the amendment adversely affects the preferential rights of any outstanding shares, any holder of such shares not voting in favor of such change may object to it at or before such meeting by filing his written objection with the secretary of the corporation and demanding payment for his shares of stock at their fair value as provided in § 623 of the business corporation law. No amendment affecting the preferential rights of any member or class of members, or any shareholder or class of shareholders, as set forth in the certificate of incorporation, shall be adopted until the written consent of the holders of two-thirds of such preferential rights has been obtained and filed with the corporation. In the case of a cooperative corporation which has adopted the delegate plan of voting at a convention, the vote to be taken as provided herein may be taken at a convention meeting and the required vote shall be two-thirds of the delegates present and voting. The amended certificate shall be subscribed and acknowledged by the president or a vice-president and the secretary or an assistant secretary, who shall annex an affidavit stating that they have been authorized to execute and file such certificate by the votes required by this section and in the manner herein prescribed.