I marked this question as a dupe. Now the OP has edited the question and added more info, so the question is not a dupe any more. How do I "unvote" to close a question?
No need. Unless others also vote for duplicate it will never close. If it does close you can just vote for it to re-open.
To make it clear, leave a comment that you voted to close but now it has changed and is not a dupe any more. Then the vote will be ignored by other users, I guess.
Can you still flag it? That way others should be able to see it and know that your vote to close as dupe is no longer relevant.
Or they'll just take note of the dupe, the now edited question and move along.