Do 50W HID ballasts eliminate the low beam error message?
 

I would think so...

I spliced in some 20w bulb carriers & bulbs and it fixed the low beam error message permanently. It provides enough resistance to fool the computer that halogen bulbs are still installed and is easy to remove when I sell and want to revert back to halogens.

On the E39 (i did exactly the same thing) I used 10w bulbs but they did not work on the e53 so I had to raise the wattage of the bulb's.