If you short out the cable then you could blow the card in the box and your modem (it's like transmitting a radio with a shorted out antenna, your outputs soon overheat (so it was you Sirius who is to blame...I'll get you back
)
Just open up the box and you'll see a solid block with 3 or 4 F sockets on it, with one of them taken up by the cable going to your house (an F socket is the same style socket as on your modem and the back of your STB that the cable plugs into) The offending cable will be plugged into one of the other sockets. Just untwist it and then if you want to just get some araldite and put a bit in each spare socket, it won't do any harm and if you need to expand your own cable in the future the VM installer will have lots of these spare.
Though this will not stop them buying a new splitter and replacing the block... You could also get a small padlock as the new grey boxes are lockable if you have one of them.