I've been around here for a little while and you would be surpised at the scope of some of the things I see. Technology questions are never bad questions.
First question- There is no way to remove the option to scroll through XM in the EX. In prior models there was a separate unit that could be removed but since 2007 Infiniti has been using an integrated XM receiver in the main audio unit.
Second question- There are really only a few voice commands on the EX.
The image below is a clipping from the manual section that highlights this.
http://www.infinitiusa.com/pdf/techpubs ... i-EX35.pdf
There is no way to say only Call X
In alternate command mode it is slightly easier to access this but you had the right idea with going with the voice tag.
You can find and edit voicetags inside the phonebook in the SETTINGS menu area.