I think you are refering the the LCM, if it fails then usually the headlights will remain on and if you turn the light selector switch nothing will happen, also your indicators may not work.
You can take one from another vehicle and put it in your however the LCM is one of the modules that records mileage and by using an already coded one from another vehicle the mileage tamper indicator will come one.
By using BMW CIP/SSS you will not be able to recode the already coded LCM, you can only code one that is "blank"/new when using BMW SSS. There is a program called PA SOFT that will allow you to recode the LCM for your VIN an Mileage, unfortunatly I don't have a cable for that otherwise I could have helped you out.