You can probably get away with it but why would you?
Because it's not as easy as flipping a breaker.
If it's unpowered there is absolutely no reason to do anything other than cut it. What are you going to do, go to where the CATV service enters the house and disconnect it? Why?
On the other hand, you know that the cable in question MAY be powered if you see a dish and sat receivers. But here again, what are you going to do- go around the house and pull all the plugs on the receivers? Would you know what a powered multi-switch is? Sure, if you knew where the cable originated you could disconnect it carefully... or kill the main breaker, that'll do it!
-Hal