The SLS height controller is just a PLIP remote replacement. I haven't tried mine while moving, but from memory the rules are:
- all doors closed
- ignition on (engine on or off)
- speed < 4kmh (I think on this one, it may need to be zero to operate, but the is a statement that standard ride height will be restored above Xkmh, which was 4 from memory)
I've used it mainly to drop and it will drop to the bump stops I think (certainly as low as I'd expect), max height I am not certain, it doesn't seem to be able to go to off road height, but I haven't truly checked.
Now, I also considered actually intercepting the height sensor voltages, but didn't progress it. It would be relatively easy to do and have a digital pot control the output voltage to the ECU. This would allow you to temporarily override the actual height. By sending ~0V it will cause it to go to max height, by sending 5V it will go to min height (or vice versa). That kind of override is very simple (in fact you don't need a micro for that, you can literally just use a 3 position switch (On-Off-On2) I reckon.
If you want middle control you need a pot, digital or otherwise. If you want to apply an offset (i.e. cause it to ride Xmm above or below the calibrated height) then you'd need a micro.
I'm open to ideas, but I would think to make a reasonably safe product for road use it would need to be a bit annoying, i.e. it will override only for Y minutes before needing reconfirming, unless the speed signal was also intercepted. I haven't checked the speed of the digital pots in any great detail, but I'd expect you might have a lag of between 1ms and 20ms from change at the actual sensor to the ECU getting a new value. That could be noticeable.

