the above statement is wrong, all bmws can be remapped.
there are many places that have done it already.
a friend of mine has done From 320, 323, 325, 335, 520, 523, 525, etc.
The tuning parameters for E9x platform are stored in the TransFlash memory of the ECU whether it's Siemens or Bosch. There are 2 ways that you can reflash the TransFlash either through OBD port or through BDM by removing the ecu and connecting the pins directly onto the CANBUS Hi/Lo pins. For ECUs that have encryption on OBD CANBUS or KLINE you can simply use the direct BDM method. There is no such thing as not being able to flash through BDM.
We would just like to introduce ourselves to anyone who may be interested in getting the ECU remapped for their BMW.
Popular Garage specializes in ECU remapping (auto only) and we have done it extensively for BMW... we sometimes have to help BMW service centres remap their client's cars before it can be fixed.
If anyone is interested, please PM us or visit our website at http://populargarage.com.my for more information.