I am considering revising an Answer I posted to a query about time resolution and bandwidth. My Answer received a fair number of positive votes -- in fact more than the accepted Answer and so I suppose that the person who posed the question didn't like my Answer. I doubt very much that he will change his mind after reading what I want to say in my revision, but that does not concern me in the least. But I am wondering about the policy of this site especially vis a vis those whose upvotes will possibly be rendered invalid after the revision if they ever get around to reading the revised version and change their minds! Are post-voting changes permitted by the moderators?
Upvotes (and downvotes) are "locked in" 5 minutes after a user casts their vote. After that, they will not be able to revoke it until the post is edited. The ability to revoke votes after editing, is in place so that downvotes placed on a poor quality question/answer can be removed if the user puts in an effort to improve it (or in some cases, revoking upvotes if they disagree with the edit).
So typically, if a user edits their post to improve it, add additional material or make typos and other corrections, no one revokes their upvotes and they're not lost either. In fact, editing to improve is always encouraged. If people happen to disagree with the user's edit, they now have the opportunity to revoke their upvote.
However, it is against the spirit of the site to edit highly upvoted answers and entirely change the content and meaning (other than for reasons in my previous point), possibly defacing it, and is not permitted. One can certainly expect downvotes to flow in if this is the case, with a high probability of a suspension.
I hope that has answered your question.