It's a counter-sunk screw. I doubt you'll be able to cut a slot in the screw without boogering the cover.
don't doubt what you have never attempted....I have succesfully done this at least a dozen times on both the brake and clutch cover screws on multiple bikes.
You need a steady hand, and position the cutter in the existing slot on the "X", carefully cut slot straight downwards it till it gets to the outer diameter of the head, this will allow a deep enough slot in the middle, due to the radius on the cutter, without destroying anything.