That’s a good question: I will check but I think this option is not visible in the user interface. On OS 3.0 or any controller that has LCD and buttons, this option can be configured manually using buttons and LCD. Usually this option is set this way: on the master controller, once you configure a remote zone, it will check the remote controller (based on the IP address you gave) to see if it’s in remote extension mode. If not, it will prompt you whether you want to set it to remote extension mode. That’s the dialog box you see. Later if you want to change the remote controller back to normal mode, you can go to the homepage of the remote controller, and it should have a red bar at the bottom indicating it’s in remote extension mode. You can click it to change it back.
The remote extension mode is a simple binary option that you can read or set through the HTTP API. However, it seems, as you observed, it’s not exposed in the UI so you can’t set it through the UI. This can certainly be changed in the future when we update the UI.