Notwithstanding the provisions of chapter 17A, in the absence or disability of the workers’ compensation commissioner, or when written delegation of authority to perform specified functions is made by the commissioner, the deputies shall have any necessary specified powers to perform any necessary or specified duties of the workers’ compensation commissioner pertaining to the commissioner’s office. Notwithstanding the definitions and terms of chapter 17A, pertaining to the issuance of final decisions, when the above circumstances exist a deputy commissioner shall have the power to issue a final decision as if issued by the agency.