It shouldn't be that hard. You can screw a couple of self tapping screws into the seal (very carefully) to help pull the seal out then wrap the shaft in ptfe tape (or similar) to protect the new seal when you drift it in .
Loads of videos on You Tube to help you out .
On the side of the throttle body you should see a screw, you can turn this to adjust your tickover. Big singles need a slightly higher tickover than most bikes or they are prone to a cough/stall especially when coming to a stop .
I did France twice on my CRF250 Rally although I don't think the WR250 is such a good travel bike , so probably yes I will. I have thought of that though and perhaps I'll just do roads on the Ducati.