I'm not sure which system you have installed.
The only hand brake I'm familiar with isn't a separate brake at all. It mounts to the foot brake lever and gives you an alternate way to operate the foot brake. Removing the foot brake lever will eliminate all brakes.
It actually mounts to the rear of the foot break setup - pushing forward on the foot brake setup behind the scenes - it doesn't actually use the "pedal portion". That said, you could remove the "pedal portion" of that brake setup without removing the out of site portion and what they ISCI Handbrake uses. That said, as discussed above and found by "IdahoMtnSpyder" - specifically as written - this would not be legal. I'd be curious to compare this to modifications to an Automobile for hand controls instead of feet controls for those that need it. I'm not sure how this would be different.