There's been a bunch of question regarding removing upvotes on comments (most of them accidental), most of which, if not all, has been closed as duplicates. However, I feel this is different.
I upvoted a comment a while back, and didn't think much of it (it was a good comment). I come back a while later, only to notice that I've upvoted a rather strange comment. After a few seconds I notice the 'edited' icon, and realize the comment has been completely rewritten, in a tone that I don't want to condone at all.
Now I can't remove the upvote. Perhaps we'd need the same thing as for other votes, and after the corresponding entry has been edited you're free to change your vote (or even flag?).