Okay, so I get it now. The extents work on the "world" as a whole, not individual noises. You have to remember that the world is being built at once, so when you move the extents, you are just moving the camera to a new area, not the noise.
That being said, you can move the "device origin" inside the device settings. You can also set it interactively in layout view using "set" button near the origin values. This would move just the noise, not the extents.