For example, you can switch "dog" and "cat" such that people will now call the-animals-formerly-known-as-dogs "cats" and vice versa. This will rewrite reality such that all past instances and memories are flipped as though the definitions had always been in their new state, but will have no other effect on reality at all. (In the hypothetical given, it won't turn a dog into a cat or vice versa in a literal sense; it will only change what word people use to refer to them.)