When you want to process a stream of data, StreamByter is the answer. MDP2 is about control. Since you already have MIDI Fire, you need to hook up your layout so that the FC-300 MIDI stream is processed by this rule:
If M0 == B0 # B0-BF for channels 1-16
If M1 >= $50
If M1 <= $60
Mat M1 = M1 + $13
End
End
End
The advanced controls example has nothing to do with what you need here.
You could do the remapping in MDP2, if you wanted to change ALL on a specified channel CC50 > 63 , etc. But it appears you want this change to apply only to output from a single device, which is where MIDI Fire excells. Each MDP2 translation requires two controls, one to receive the desired Cc, supercontrol, driving a second subcontrol with the desired output Cc.