“PA does NOT have early voting”
But they do have absentee voting
However, unless the law has changed since I was a judge of elections eight years ago, here is no way to "change" an absentee vote.
You can override your absentee vote by appearing in person at the precinct polling place at which you are enrolled. There, you must present two forms of ID, and if the judge, any clerk, or any person present challenges your vote, your ballot will be accepted as provisional, and will be hand counted within two weeks following the election.