The Maximum AUW is part of the aircraft certification. If you operate above the certified weight then the Certificate of Airworthines is invalid - Offence No1. If the C of A is invalid then the insurer would almost certainly say trhat you were outside the terms of the policy which of course is now mandatory - Offence no 2. Now depending upon the circumstances it could be considerd that you were endangering the aircraft, the passengers and people on the ground; that could ammount to two further offences.