Possible, yes, probably one of the easier IP seals to replace with the IP installed. If you have successfully done headgasket, cambelt, IP timing, and injectors, you have proven your abilities. IP throttle shaft seal is similar skill level, but more like working on a sewing machine.
I thought I had bookmarked some pictorials but cannot find them, here is a link that has helpful photos and descriptions (note the bracketry and springs are different, as are some of the pieces in the governor spring assembly):
http://www.vwdiesel.net/forum/index.php?topic=24323.0
Ball-end long allen wrench (5? or 6mm?) is strongly suggested to remove the IP cover screws.
Some important points:
1. Clean area as best as possible, leave IP full of fuel (don't drain) so dirt on the edges will tend to spill out rather than fall into the IP.
2. Mark (scribe) position of accelerator lever on splined throttle shaft before removing.
3. Recommend removing fuel screw before removing IP cover. Makes reassembly easier. Count turns to full seating, to arrive at same position on reassembly.
4. Note orientation of gov. assy. (where the elbow is pointing) in underside of IP cover. You will need to repeat this orientation on reassembly.
5. Throttle shaft may need some sharp hammer taps to convince it to slide out of the bushing.
6. If you remove the gov. assy. from the fulcrum lever, make sure you get it connected up correctly when replacing the cover.
7. Might as well replace the IP cover seal while you have the cover off. Also the fuel screw o-ring.
8. Reinstalling the IP cover can be bunglesome. Need to worry about orientation of gov. assy. and matchup of fuel shutoff lever to corresponding piece in IP cover. Cover should drop into place with no forcing. IP cover screw torque is not that high; it is the rubber seal that does the sealing, not metal to metal.