1. In the US, the supreme court has repeatedly held that the ex-post-facto clause only applies to criminal laws (See Calder v. Bull, which was decided in 1798).
This is actually consistent with the history of the clause (It was understood to apply to criminal laws. Motions were made to change the wording to say it also applied to civil cases, they were turned down)
2. This is not a law, and may not even be administrative rulemaking (depending on what exactly they issued)
Of course, even if it was, you have a mechanism to challenge it if they hold you to it: the courts.
This is actually consistent with the history of the clause (It was understood to apply to criminal laws. Motions were made to change the wording to say it also applied to civil cases, they were turned down)
2. This is not a law, and may not even be administrative rulemaking (depending on what exactly they issued)
Of course, even if it was, you have a mechanism to challenge it if they hold you to it: the courts.