Any of the foregoing rules may be waived by stipulation of the parties concerned with the consent of the commissioner. If a hearing has been convened, such a waiver or stipulation shall require the consent of the hearing officer. The commissioner, or the hearing officer acting in his behalf, may waive any of the aforesaid rules; provided, however, he shall not waive those rules pertaining to the service of notice of hearing and service of the final order and determination.