I don't think that most consumers of these books will know that modern changes have been made. And I think that most of them would be less willing to pay for copies with these changes. So they're being mislead for increased profit.

Even in the US, the First Amendment doesn't protect false advertising. I don't think making these changes without informing the buyer would be illegal under current law, but I don't think it would be unconstitutional to make it illegal, not would it contravene the spirit of free speech.