A screwdriver can only be recommended for those who have a steady grip.
All others please use the special tool.
When the screwdriver slips from the slot there is a real chance the rear element of the lens will be damaged.
When using the wind crank does not work (either 'normal', or using the double exposure unlock button), you don't.
Putting anything through the film gate, where it may collide with the shutter curtains, is a bad idea.
You can't use a screwdriver/cocking tool anyway, since the axle is covered by the camera's inner bottom plate.
I haven't had a problem as long as i have been using focal plane shutter Hasselblad cameras (not with the 500-series cameras either, except for one time, caused by a automatic bellows that was known to have a problem. Then the screwdriver was of help, after demonstrating the fault to the repair person).
But even should there be a problem: there's nothing you can do yourself, except try the wind crank with double exposure button pressed.