I did this earlier this summer and here's my procedure. Took about 15 minutes.
1. Lube new cable.
2. Remove old cable ends from lever and gearbox.
3. Using electric tape, tape the end of the old to the front of the new cable. Have enough over lap so the link doesn't break free.
4. Pull old cable out and new cable in. Start under the tank if you can. Go back and forth from the head light, under the tank pushing and pulling the cable chain into position. Watch for the cable getting caught up under he tank and in the nacelle. I didn't open the head light but you could.
5. Once in position, connect both ends of the cable up. Adjust in the back, and then fine tune up front.
It took some back and forth fiddling, but it worked fine.
Hope this helps!