I would say that the short answer is no, you dont need to discharge the crt.  All the work you'll be doing is on the other side of the analog display assembly, so you wont be near the anode aperture, or anode cap. The closest you'll get will be removing the main rear fan assembly. So, bearing that in mind, pay attention to what you do touch, make sure not to touch other things, and you should be all good.

however, should you want to discharge that puppy, got a long handled screwdriver, and some wire with alligator clips. clip one end to the screwdriver, and the other end to the heat sink on the computer's chassis. Use the screwdriver to pry up the anode cap, and rub its contacts thoroughly. then, do the same to the anode aperture. Be careful though, as you dont want to be wearing a wrist strap when doing this. likewise, if you let it sit, you may want to discharge again, since the charge can build back up.
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Electricity tastes good. No, seriously.