retroact

verb

1. To act retrospectively or in opposition

   “In their eyes the past was good or bad for itself, and the present good or bad for itself, and an evil past could no more shadow a virtuous present than a virtuous present could retroact to brighten or redeem an ugly past.”

2. to be retrospective.
3. To apply (a law) retroactively to situations that predate the enactment of the law.

   “Sec. 4. The effectivity of this Act shall retroact to January 1, 2001.”