This is what happens:
1) change .urls as described in the quoted text
2) once the screen refreshes, the .jpg and .gif icons are no longer visible. Instead, you see a bunch of RED [X] (placeholders + broken images).
3) trying to change things back to the IP address does nothing - click any link in CP.cgi and you see the main cp.cgi screen
4) starting a new cp.cgi session - cannot log in.
5) to fix this - manually edit vars_config.cgi file