In the old days, the analogue systems had filters (often) installed at the customer side (maybe at the box just outside your home) to scramble the signal. You could just remove those (or the installer could forget to install it) and get the channels.
The cableco programs the digital boxes and they have 2way communications so the installer guy is not going to be able to get you free channels. There is a device on ebay, that supposedly blocks the return path, but there were news stories (a few mo's ago) on how after a month or so the signals were received from the cable co and the customers ended up w/ large bills... and some legal problems. The devices didn't do what they needed to, and/or after a month or so the box shuts off if it can't get thru. When cable co comes out to fix or you want to replace it, etc, you pay $$$.
One time, a neighbor of mine was having cable installed. The cable guy offered to get him some extra channels, etc. the neighbor asked if he could come back later. When he did, the cable guy found out he offered extra channels to a cop... and was busted. (That was in the old days mentioned in first paragraph).