(1) The power of the Minister under this Act to make a determination or give an approval includes the power, by writing, to revoke or vary a previous determination made, or previous approval given, in the exercise of the power.
(2) An instrument that is expressed to revoke a determination as previously varied, or to revoke an approval as previously varied, has effect as the revocation of the determination or approval and of every later instrument so far as that later instrument varied the determination or approval or varied the determination or approval as previously varied.
(3) An instrument that is expressed to vary a determination as previously varied or to vary an approval as previously varied has effect according to its terms even though it does not specifically refer to the previous instruments of variation.
(4) The one instrument may contain one or more revocations or one or more variations, or both.
(5) An instrument of revocation or variation takes effect on:
(a) the day stated for the purpose in the instrument; or
(b) if no day is stated--the day on which the instrument is made.
(6) The day of effect of an instrument revoking or varying a determination or approval may be a day before the day of the making of the instrument only if the provision under or for the purposes of which the determination or approval was made or given permits the determination or approval to take effect on a day before it was made or given.
(7) Subsection ( 6) has effect despite subsection ( 5).