Towing Question for Mr. Cavo

I had a mariner call me and ask this question:

A mariner holds a Master of Towing Western Rivers and a Mate(Pilot of Towing) Inland restricted to 200 Tons. He is operating as a Mate on a vessel of 400 GRT on Inland waters. I know that he shouldn’t be because he is restricted to the tonnage on the Mate’s license and the route on the Master’s license. Is there any CFR stating that a Mate can’t operate a vessel of 400 GRT if he is restricted to 200 GRT and he can’t Master because he only has a Western Rivers route, not Inland. Also, can you tell me what the easiest, well best way to go about operating this vessel legally is?