It's not that difficult--in theory. Four bolts to drop the driveshaft, and one big ass nut that holds the pinion flange on, slide off pinion flange, pry off old seal. Install is basically reverse of removal. The tricky parts are:
1) Do you have/can you get a socket for that nut (I forget the exact size, but it is something like 24 or 27MM)
2) Getting the new seal back on without damaging it. If you have changed a seal before, chances are that the shaft you are sealing was not installed at the time (i.e. you remove the axle to change the axle seal, or you remove the hub from the spindle to change the wheel bearing seal). On a diff the pinion shaft is still there, which makes seal installation more difficult.
3) Here is the trickiest part: The procedure for tightening that big ass nut is not to a torque spec, but a preload value. Basically you tighten it until you get a certain amount of resistance when turning it. Too loose or too tight could destroy your diff after a while. What I did on mine several years ago (because I had no way to measure the preload at the time) was to just keep tightening a little at a time (like 1/8 of a turn) until I got a slight increase in drag when turning it. After driving it a bit it got noisy, so I went back under the car and found it was spinning too easily, so I tightened it a little more. After that , it worked fine for years. I just took this diff out last weekend and it still looks great after about 75,000 miles.
I would say you could do it IF you are relatively mechanically inclined, have changed some kind of seal before, AND are open to the possibility of damaging this diff (like you can get another one at a pick a part if you mess this one up). Otherwise have someone do it.
I hope this helps.