This is not a duplicate of What is the justification for locking votes?. It doesn't address the suggestion brought up here to allow a certain limited quota of "unvotes" per week.
It happens rarely, but sometimes new information comes to light on posts I have voted on that make me want to change my vote - for example, a comment may provide new information, or may bring up a different perspective I hadn't considered.
Currently, I can not change my vote after a certain period of time, after which it is "locked in". The only way to change a vote once it is locked in is by editing the post.
That's a harmful workaround, as it bumps the question to the top. Also it's an unfair workaround in that users without editing privileges can't apply it.
Users should be allowed to change one locked-in vote per day.
This should account for most erroneous votes, while still preventing the possible misuse that is the reason why the lock exists in the first place.