((a)) The Secretary concerned and, when designated by him, any Under Secretary, Assistant Secretary, Judge Advocate General, or commanding officer may remit or suspend any part or amount of the unexecuted part of any sentence, including all uncollected forfeitures other than a sentence approved by the President. However, in the case of a sentence of confinement for life without eligibility for parole that is adjudged for an offense committed after , after the sentence is ordered executed, the authority of the Secretary concerned under the preceding sentence (1) may not be delegated, and (2) may be exercised only after the service of a period of confinement of not less than 20 years.
((b)) The Secretary concerned may, for good cause, substitute an administrative form of discharge for a discharge or dismissal executed in accordance with the sentence of a court-martial.