E61's have dual rear side/tail light bulbs with the outer one also operating as a brake light, does anyone know if it's possible to code out one of the sides light bulbs ? Specifically the one that also operates as a brake light.

I want the outer bulb to be just a brake light and have the inner bulb as a side/tail light.

If it can't be coded i'm guessing i'm going to have to Frankenstein the light cluster

 

I think not and you might be better of with re-wiring. As you said, the outer bulb is tail light + foot break; inner is tail light + flashing ABS brake (when it activates, unsure if it actually flashes). Hope this helps!