score:3
As it stands (based on information I got from phone calls with the HSE and Irish Citizens Information) one is bound by the rules that were in place on entering the country, unless any official source would explicitly state otherwise - which so far has not been the case.
In short, if you're subject to restrictions of movements when you arrive, they stay in place even if the country is cleared in the meantime. Similarly, you won't have to go into movement restrictions if you came from a country on the Green List that is taken down from there within two weeks after your arrival.