What is the interference? Have you tried changing the channel of the router you currently have to be as far from the new one as you can be?
I wouldn't mess too much with it, should it not work down the road they will most certainly blame the reconfiguration of their router as to why the alarm did not work.
Also see this thread as to why they don't want you doing what you want to do with their set up
http://forums.comcast.com/t5/Devices...s/td-p/1254975