Section 6. Subject to appropriation, the secretary, with the approval of the governor, may appoint such experts and other assistants as he shall deem necessary to perform the functions of his office, provided that the provisions of chapter thirty-one and section nine A of chapter thirty shall not apply to any person holding any such appointment. Every person so appointed to any position in his office shall have experience and skill in the field of such position. So far as practicable in the judgment of the secretary, appointments to such positions in his office shall be made by promoting employees of the commonwealth serving in positions which are classified under chapter thirty-one, and such appointments shall at all times reflect the professional needs of the department or division affected. If an employee serving in a position which is classified under chapter thirty-one or in which he has tenure by reason of section nine A of chapter thirty shall be appointed to a position within his office which is not subject to the provisions of chapter thirty-one, he shall upon termination of his service in such unclassified position be restored to the position which he held immediately prior to such appointment; provided, however, that his service in such unclassified position shall be determined by the civil service commission in accordance with the standards applied by said commission in administering chapter thirty-one. Such restoration shall be made without impairment of his civil service status or tenure under section nine A of chapter thirty and without loss of seniority, retirement, or other rights to which uninterrupted service in such prior position would have entitled him. During the period of such appointment, each person so appointed from a position in the classified civil service shall be eligible to take any competitive promotional examination for which he would otherwise have been eligible.