The applicant shall file with the Commissioner at the time of furnishing the bond a schedule of his maximum commissions and charges for service in connection with the produce handled on account of or as agent for the parties. Such commissions and charges shall not be changed for one year thereafter, except by a written contract between the commission merchant and the consignors of farm products. A person operating a livestock auction market or stockyard that has been posted by the U.S. Department of Agriculture and is being operated pursuant to the provisions of the Packers and Stockyards Act of 1921 (42 Stat. 159), as amended, may change his schedule of maximum commissions and charges if such changes are filed with the U.S. Department of Agriculture and are approved. These changes shall be posted with the Commissioner.