8. The provisions of this undertaking shall take effect once the merchant begins to use the exemption prescribed in section 91.4 of the Regulation respecting the application of the Consumer Protection Act (chapter P-40.1, r. 3) and they shall cease to apply on the date on which the merchant ceases to use that exemption provided that he notifies the president of the Office de la protection du consommateur of that fact in writing at least 15 days before that date.