Up until Oct 19 when they shut down the online voter registration system, anyone could change any citizens' voter registration online - without their knowledge or consent. Also, you can see whether or not they voted absentee.

Effectively, by changing voter registration before 30 days of the election you spoil an absentee ballot. You can also make it so they're not on their local voter role on election day & the local clerk would have to update it. Imagine in a large district - having to fix 10s of thousands of incorrect voter registration information before someone can vote. Effectively causing a physical denial of service on someone's ability to vote.

EDIT: I find the Secretary of State change of tune very suspect because she said this 2 days after I disclosed this directly to the Michigan Bureau of Elections and within an hour of me disclosing the issue with EVERY representative of Michigan in the State and Federal legislature.