Update PX4Flow's transmittbuffer for further communication (i2c) with pixhawk

Hey guys,

this is a bit complicated to explain. I tried several times to extend the transmittbuffer (update_TX_buffer) for I2C.
Therefore i added like a dummy variable to the code, extended everything necessary in the PX4Flows Firmware and built it.
Now i wanted to adjust ArduCopter to recieve/work with the additional data. But i encountered multiple problems in terms of building it afterwards.
So my question to u know is: Did someone already achieved to do sth similar? And how?

Best regards