Yes you can move the Cable box power key to the TV group, and then change the aux device to something else.
The 994 command creates a small list in the C7 memory, the first two bytes indicate the button and device key you are copying/storing into, the next three bytes indicate the device type copied from, the specific device code that was assigned to the device at the time you created the assignment, and the data to transmit. The device code that was copied does not need to remain assigned to any device key.
The Cinema 7 has room to store about 45 key moves if you do not have any macros programmed. Learned codes are in a separate area, so they don't take memory away from the advanced codes/macros.
There is a group of people who have been able to add device codes (like ReplayTV and Tivo) to the Cinema 7 and Rs 15-1994. Check this forum for threads about the JP1 interface or JP1 box, or look at Rob Crowes website
[Link: hifi-remote.com]