I believe the consequence for trying to go beyond their limit is a suspension fault and a dumping back to Normal Height. As far as I know, the current method of modifying the sensor arms allows you to go to what once was "Super Extended Mode" and that's it. If you mess around and hold the toggle with your foot on the brake while in that mode (which would just be Extended Mode in the rod-mod definition) then you'll get a fault.
I'm not sure that was very clear...but at the end of the day the air bags are still working within their original parameters with the rod-mod and nobody has ever breached that limit.
Moving on, I'd like to hear more about the lift that Nathan's post refers to. That picture looked like an LR3 in Extended Mode sitting next to an LR3 in Normal Mode, although that's not what it purports. To say that it can go higher is nutty! Spacers? Where would they go? There are no coils or leaf springs so where the heck would the spacers go in that sort of lift?