[1]: https://www.congress.gov/bill/115th-congress/house-joint-res... [2]: https://techcrunch.com/2017/10/24/congress-votes-to-disallow...
Upon quick searching, it looks like scholars have debated the civil/criminal point:
https://www.quora.com/Does-ex-post-facto-apply-to-civil-and-...
https://en.wikipedia.org/wiki/Ex_post_facto_law#United_State...
However, it's not symmetric - lifting prohibitions can be done retroactively, to not prosecute people for things they did back when it was still prohibited.
Unfair, arbitrary prosecution may violate someones rights, but unfair, arbitrary immunity can not - there's no right to get someone else punished.
What about a Federal program?