For criminal concerns regarding retroactive ITAR additions, yes. However, significant civil financial penalties if congress so wished could still be constitutional as the ex post facto clause has been held to apply exclusively to criminal matters starting in Calder v. Bull [1].

[1] https://www.oyez.org/cases/1789-1850/3us386

Dogs can't play basketball, either, but we've sure been getting dunked on a lot lately.

> explicitly banned in the US Constitution

There are a lot of things in the US Constitution. But the Supreme Court is the final arbiter, and they're moving closer and closer to "whatever you say, big daddy."