Any disbursing agent of the Indian Service, with the approval of the Commissioner of Indian Affairs, may authorize a clerk employed in his office to act in his place and discharge all the duties devolved upon him by law or regulations during such time as he may be unable to perform the duties of his position because of absence, physical disability, or other disqualifying circumstances: Provided, That such clerk, while acting for his principal, shall be subject to all the liabilities and penalties prescribed by law for official misconduct of disbursing agents.