If you are so concerned about the amount of MSing that you are doing on a card to the point where you may be shut down, then you (not the card provider) should be proactive in draining that account of its rewards immediately after the points/cash is posted. They can't claw back what isn't there.

The problem isn't the MSing (since everyone is at risk for a shutdown), rather the problem is leaving the rewards where they can be confiscated