If I tell the children "from now on fruitcake is banned in this house", changing the law of my household, does that mean I have changed? Does that mean my children cannot know what is right and wrong and will be confused about how I expect them to behave?
You're taking this too far. Nobody is suggesting that God has ever made a drastic reversal in the law, "adultery was once a sin now it's ok". That's a straw-man argument.
But He has altered his instructions for his people over time. Adam was told to eat vegetables, Noah was told he could eat animals also, then the Israelites were told through Moses that they couldn't eat pork. Even if you assume that Noah was actually told not to eat pork also and it just wasn't written in scripture clearly (as most Torah-keepers will argue, insisting this law was permanent and reading it back into the preceding chapters as a result), it's very hard to see the change from Adam's vegetarian diet to Noah's omnivorous diet as anything other than a change in the law. But it's only a modification, not a reversal.