The Administrator, on appeal on petition for review, shall afford a reasonable opportunity for the submission of proposed findings, conclusions or exceptions with reasons in support thereof and an opportunity for oral argument. He may alter or modify any finding of the administrative law judge (or of the appropriate TTB officer in application proceedings) and may affirm, reverse, or modify the decision of the administrative law judge (or of the appropriate TTB officer in initial application proceedings), or he may remand the case for further hearing, but he shall not consider evidence which is not a part of the record. Appeals and petitions for review shall not be decided by the Administrator in any proceeding in which he has engaged in investigation or prosecution, and in such event he shall so state his disqualification in writing and refer the record to the Under Secretary for appropriate action. The Under Secretary may designate an Assistant Secretary or one of his principal aides to consider any proceeding instead of the Administrator. The original copy of the decision on review shall be placed in the official record of the proceeding, a signed duplicate original shall be served upon the applicant or respondent and a copy shall be transmitted to the appropriate TTB officer. When, on appeal, the Administrator affirms the decision of the appropriate TTB officer or the administrative law judge, as the case may be, disapproving an application or suspending, revoking or annulling a permit, such action shall not supersede the decision of the appropriate TTB officer or the administrative law judge and such decision shall be final.