Mich. Comp. Laws § 123.960
Amendments may be made to articles of incorporation if adopted by the legislative body of each incorporating unit: Provided, That no such amendment shall impair the obligation of any bond or other contract. Any city or village which is the county seat of a county incorporating an authority under the provisions of this act, may become an incorporating unit of the authority by amendment to the articles of incorporation adopted by the legislative body of such city or village and by the legislative body of the county. Any such city or village shall thereafter be deemed to be an incorporating unit. Each amendment shall be adopted, executed and published, and certified printed copies filed, in the same manner as above specified for the original articles of incorporation, in so far as applicable.
MCL 123.960