That Thom & Co. have to capture a Finn leader with the forbidden items (musicbox & fireworks to stun, cuendillar chains to bind) and then exchange prisoners, the Finn for Moiraine. This would be the ultimate breaking of the rules, since in Snakes & Foxes, the Finn try to capture the human piece. Of course, Mat has to cut out his left eye before, so that his link to the Aelfinn will be severed.