most pilots would have difficultly knowing how to switch it off.
A little research:
SDU (SATCOM) is powered by Left AC Bus
Other systems powered by this bus are not documented (BDL Bus Distribution List not available for 777) as far as I can see... that is if you lose it that's when you may find out (some items not EICAS messaged on fault)
You can piece together from Maintenance manuals but not in one place.
E/E bay access likely needed for CB, then straightforward, 3 CB's.
Looking at the docs access to the SDU via E11 rack could be achieved in the cabin also (not sure about this as I don't know how easy it would be to access).
Disabling from the Cockpit... unlikely.
Disclaimer: I'm not an Engineer.