Don't think the extreme is that much different from the Ultra. Here's how I do it :
Installation-Channel Scan, hit OK, then down-arrow to highlight the line that starts with EDIT TP.
Arrow-right until it highlights ADD SAT, push OK..ARrow right again until RENAME lights up, hit ok to get the keyboard to rename it to whatever you want. When done , F2 saves it, then EXIT out. Go to Satellite setup then to set the parameters, switch positions etc for that satellite (be sure the one you added is the one showing in the title bar)
If not exact, then the extreme you have should be pretty close. They DO hide the dang ADD SAT thing in a funny place!