I'm not sure I fully understand your question.
If someone revises their upvote, then the original upvote is removed and the new upvote value is applied.
For instance, if I upvote 100% then later change it to 0%, the author gets nothing and I get nothing. However, I do not get my upvote manna back, so zeroing out my upvote takes those author rewards away from the author and also takes those curation rewards away from myself.
I believe u understood quite well, even if I was sleep deprived rambling and couldn't fully form coherence.
Ty, answered well.