This would basically function as a zero-day suspension: the reviewer would get the message in exactly the same way they would for a review suspension, except that they can keep reviewing afterward.
Background: It's not uncommon to see bad reviews where the user is simply mistaken about how some aspect of the review system should be used. They're not robo-reviewing or approving blatant spam edits; they just maybe haven't read all of the meta posts that could have advised them better.
As (tragically overworked) moderators (who need all the good help we can get), we don't actually want these people to stop reviewing. We just want them to change one particular aspect of how they're reviewing. We could send a moderator message to them, but since we already have a system for warning about bad reviews, it would be much better to use that system instead (and it would avoid spamming other moderators with noise about bad reviewing that they probably don't care to read).
This would be in line with our approach to correcting other behaviors on the site: we often mod-message a user without suspending for a first offense, in the hope that a "hey, stop doing that" will correct the behavior—and it often does. We should be able to do the same for reviews.