Yea this is pretty easy. Just modify the xml code for Watch Television. You will see the following format. (Sorry if the formating is very good.)
11995
999
WXIN
Dislike
11877
998
WTHR
---repeated for all channels
Just change the name, channel id, order, etc. You can find the station id's on the harmony site by adding a new channel (at the bottom). If you can't find the id (only used if you are using the tv listing guide) then just pick a number higher than 50000 that you haven't already used. If you don't want the channel to be hidden then just remove the preference line.
-Jason