After casting a vote on an answer, you can change your vote during a small time window, but afterwards the change is blocked by the error:
Vote too old to be changed, unless this answer is edited (click on this box to dismiss)
Sometimes my past votes are clearly wrong, and I'd like to correct them. If I understand the other Meta questions correctly, vote changing was disabled due to concerns about cheating or tactical voting.
Would it be an option to allow changing your vote at a cost to your own reputation? I'm not sure about the exact nature of the tactical votes, but it seems to me that the cost of reputation could outweigh the advantage of tactical voting.
For me, I don't care greatly about reputation, but I do care about my old wrong votes permanently affixed to an answer.
P.S. Apparently I can change my vote by editing the answer, but that feels wrong (the answer gets a later timestamp), and might not be available to every user.
P.S.2. One of my best experiences in Stackoverflow was when I posted an answer, and instantly got downvoted to -5. Then someone with high rep upvoted me and commented "hey this is actually correct". Many people changed their votes and my answer was eventually accepted. Such an experience would be impossible now.