Not an answer to your question, but I am thinking about doing the opposite (kind of). I want to let it expire and then wait for all data to be gone. Fix all of my album art and then re-subscribe so that all of the correct album art gets uploaded right from the start.
When I originally signed up not all of my art was correct, so what was matched and uploaded was not correct and now i have found no good way to update what is in iTunes match.