Does a retroactive change in the criminal code violate the ex post facto clause of the Constitution?

To violate the ex post facto clause of the Constitution, a law must be retrospective and it must disadvantage the offender affected by it. Weaver v. Graham, 450 U.S. 24, 29, 101 S.Ct. 960, 964, 67 L.Ed.2d 17 (1981); United States v. Crozier, 777 F.2d 1376, 1383 (9th Cir.1985). Furthermore, "[e]ven if a retroactive change in the law is a disadvantage to the criminal defendant, it does not violate the [ex post facto ] clause if the change is procedural rather than substantive." United States v. McCahill, 765 F.2d 849, 850 (citing Dobbert v. Florida, 432 U.S. 282, 293, 97 S.Ct. 2290, 2298, 53 L.Ed.2d 344 (1977)).