It's a while since I have removed one but I think I just get two screwdrivers opposite one another and lever the sprocket up.
This is the way to remove the generator sprocket, two drivers under the boss, not the teeth, and lever up.
Most generators I have seen have the thread on the shaft ruined by butchers with big hammers.
Trev.
If removing the generator sprocket, leave the nut on the shaft loose. This saves searching for the sprocket when it flies off.