Hi Pierrot
well, you say changing the battery type is possible so changing the brake should be possible, too.
It´s the same kind of programming.
If there is really no chance to change the brake I believe your controller is out of order 
Please contact your local dealer or call the MULTIPLEX service dept. They will help you. If the controller is within the warranty period it will be changed.
https://www.multiplex-rc.de/service/service-adressen.html
Best regards,
your MPX Team