No, an ex post facto law would be one that said that if you possessed it before the law passed,you are guilty of a crime.
If you purchased it when it was legal you committed no crime but the new law would automatically make you a criminal. An ex post facto law is one that takes effect before it is passed, a retroactive law. What if the change wasn’t made public, as is often done in third world countries? You could “disappear” in the night and never be seen again. It happens.
Eminent domain is the taking of private property for public use (screw what SCOTUS did in Connecticut) and you must be fairly compensated. But even if ‘for the public good’ qualified, you still are not a criminal and must be compensated, else the government is the criminal, guilty of theft.
Why do we put up with this? We number over three hundred million and yet we allow a handful of legislators and congressmen to bring us to our knees. It has to stop and I, for one, am ready to fight.