if you press "Show DevMode options" and then make it "Active" then press "Select another starting location for the player" It will put out an error and make you not be able to use the editor anymore.

The tab will even change to undefinable during the loading screen.

You can still download unless you have a slow Wi-Fi and you cannot download large files within 100 seconds, after 100 seconds the site will time out the download. You'd have to download it so you can edit it in Quest Software.