No problem to do it, You might have to drop the manifold pipes, remove shifter, (be sure to mark the shifter & shaft with a marker before you remove the shifter, helps to get it back in the same spot)
Pick out the old seal with a piece of wire or sharp pick/screwdriver.
Cover the shaft splines with tape & replace the new seal. remove tape & shifter. :waving:
Generally, you won't have to drop the left exhaust header, but smoe bikes are a little tighter than others for getting the shifting linkage back on the shaft there... One common 'trick' is to leave the seal loose (not pressed into the case, but threaded onto the shaft) as you go to reinstall the shifter link. That'll afford a little extra play in the shaft for reassembly -- "wiggle room" if you will...
There is variance amoungst bikes for the Gap between the end of the shift lever and the frame... which can lead to trouble removing the shift lever.
If that happens with yours, then have on-hand a small Grinding Wheel (1/8" thick x 3/4" diameter) and Dremel tool, to reach in and Remove a slight amount of material from the end of the shift lever, to gain clearance... I had to remove about 0.030" ...once you do that, then the problem is solved forever after.