Mich. Comp. Laws § 450.1782

Sec. 782. (1) Whether or not a business combination is authorized or consummated in whole or in part after the effective date of this chapter or after the interested shareholder became an interested shareholder, the requirements of section 780 shall not apply to business combinations that specifically, generally, or generally by types, as to specifically identified or unidentified existing or future interested shareholders or their affiliates, have been approved or exempted from the requirements of section 780 by resolution of the board of directors of the corporation pursuant to either of the following: (a) Not later than 4 months after the effective date of this chapter or an earlier date as may be irrevocably established by resolution of the board of directors. (b) If involving transactions with a particular interested shareholder or its existing or future affiliates, at any time prior to the time that the interested shareholder first became an interested shareholder. (2) Unless by its terms a resolution adopted under this section is made irrevocable, the resolution may be altered or repealed by the board of directors, but this action shall not affect any business combinations that have been consummated, or which are the subject of an existing agreement entered into, prior to the alteration or repeal.