A carrier shall be at liberty to surrender in whole or in part all or any of his rights and immunities or to increase any of his responsibilities and obligations under these Rules, provided such surrender or increase shall be embodied in the bill of lading issued to the shipper. The provisions of these Rules shall not be applicable to charter parties, but if bills of lading are issued in the case of a ship under a charter party they shall comply with the terms of these Rules. Nothing in these Rules shall be held to prevent the insertion in a bill of lading of any lawful provision regarding general average.