Some days ago my new metal extruders and a dual extruder arrived.
So the old extruder had to be disassembled from my Prusa I3B pro to add it for some tests to my new MPCNC machine.
The dual extruder replaced the single one and magically the Prusa I3B pro became a Prusa I3C Pro. First tests with printing dual colors at the same time were succesful. Simply changing the firmware from I3B Pro marlin to the I3C Pro marlin did the thing.