If you have no Internet, the webpages won’t render correctly, so you can’t change any settings through the web interface. But you can still send http command. Basically the Javascripts are used to render the webpages, and to construct an HTTP GET command to send to the controller. If you know how the HTTP GET commands are constructed, you can send it without the webpages at all. The list of commands are documented here:
http://rayshobby.net/?page_id=730#httpget
It is very technical, so I don’t expect anyone to use these commands manually (unless if you write a program to do it).