(1) Subject to such restrictions, reservations or conditions as may be contained in any warrant issued under section 153 or section 154 and to the provisions of sub-sections (2) and (3), a confirming authority may, when confirming the sentence of a court-martial, mitigate or remit the punishment thereby awarded, or commute that punishment for any punishment or punishments lower in the scale laid down in section 73.
     (2) A sentence of transportation shall not be commuted for a sentence of imprisonment or detention for a term exceeding the term of transportation awarded by the court.
     (3) A sentence of imprisonment shall not be commuted for a sentence of detention for a term exceeding the term of imprisonment awarded by the court.