Lowering an air suspension is a relatively simple thing. Lowering links are available on eBay for most BMW and Mercedes air suspension cars and SUVs and most motorbikes.
BMW x5 4 8IS lowering Links Module Fully Adjustable | eBay
All these links do is trick the car into thinking the ride hight is a few inches higher than it really is.
The system that controls which height is set for each speed is not changed so the car will still go to standard and low at the same transition speeds. The only change is that each level will now be lower by 2 inches (or whatever is set on the lowering link).