I changed out cable boxes from a motorola DCT-6416 to a DCX3400. I've looked through all the settings, but cannot find anywhere to change the cable box model so that when I press the "off" button on the harmony remote, that everything (including the DCX3400) will turn off. Is this change as simple as going into the settings and renaming it?

Go into 'Devices', remove the old cable box and add the new one. It's in the data base: http://myremotesetup.com/EasyZapper/New/Main.asp

Then redo the 'Activity".