According to foxnews, in at least four states in the U.S., it is possible for early absentee voters who have already voted to recast of cancel their ballots. Among these states are Pennsylvania, Wisconsin, and Michigan, but the rules vary from state to state. In Wisconsin, for example, absentee voters can change their ballots as many as three times before election day. Wisconsin GOP Rep. Sean Duffy fears that after the re-opening of the Clinton email investigation, that many absentee voters will change their ballots from Democrat to Republican. Roughly 22 million Americans have already cast their vote through absentee ballots, mail, or at the polls. Pennsylvania allows its absentee voters to change their mind by voting in person on election day. "The really important one is Pennsylvania because that is one of the states that Donald Trump says is a must-win for him," says political analyst Erin McPike. "That is the real state to watch." The fourth state, Michigan has voted Democratic every presidential election since 1976 and allows its absentee voters to cancel their ballot, request a new mail-in ballot, and vote in person before 5 p.m. on November 7 or vote on election day.
http://www.foxnews.com/politics/2016/11/01/early-absentee-voters-can-still-change-ballots-in-at-least-four-states.html