Nonsense, there's no gears on the XT's they just go from off to full on, very little in between... or too short to notice.
On a serious note you can change sprocket size but these involve a number of issues:
- new longer chain
- your speedo reading will be inaccurate and you will need to fit a speedo healer to readjust it
- whatever you add in the long run you take off from the bike low end torque, and torque can be a life saver when you need to speed out of a dangerous situation.
Have a look at the attached spreadsheet to see the effect of tooth removal / increasing on your sprockets.