Cutting an X in the top of lead bullets goes back at least to the days of the Wild West, and perhaps to the Civil War. I've never heard of anyone doing that will FMJ bullets. The experiment should be cheap enough... the cost of a single round. If it doesn't work out, just throw it away.
That said, be sure that scoring the top of your FMJ round doesnt' deform the bullet's circumfrence. You don't want to risk increasing chamber pressures any higher than they already are.
Scott