Mich. Comp. Laws § 700.2205: Waiver of rights by surviving spouse.

Sec. 2205.

The rights of the surviving spouse to a share under intestate succession, homestead allowance, election, exempt property, or family allowance may be waived, wholly or partially, before or after marriage, by a written contract, agreement, or waiver signed by the party waiving after fair disclosure. Unless it provides to the contrary, a waiver of "all rights" in the property or estate of a present or prospective spouse or a complete property settlement entered into after or in anticipation of separate maintenance is a waiver of all rights to homestead allowance, election, exempt property, and family allowance by the spouse in the property of the other and is an irrevocable renunciation by the spouse of all benefits that would otherwise pass to the spouse from the other spouse by intestate succession or by virtue of a will executed before the waiver or property settlement.