It assigns a key of your choosing to be the thumbs down command. Advanced code 00245 is the thumbs down command. Other tivo advanced codes are here:

[Link: hifi-remote.com]

You will have to add two zeroes to the front of each advanced code in that link, since the 8820 only takes 5 digit advanced codes(another name is EFC).

The EFC's may look different, but there only 256 available EFC to a setup code, 00000-00255. After 00255 they repeat. So 00000= 00256= 00512 and so on.