After filing of the written notice of disciplinary action, it may be withdrawn by the Appointing Authority at any time prior to the final decision of the Personnel Board. An amended notice may be filed by the Appointing Authority at any time prior to the commencement of the hearing before the Personnel Board. If an amended notice of disciplinary action presents new causes for discipline, the employee shall be afforded a reasonable opportunity to prepare the defense thereto and must file an amended answer within ten working days of the receipt of the amended notice.