A pilot probably wouldn't know how all the systems work together. (They probably know what ACARS and ADS-B -do-, but not the implementation details.) You would want an avionics engineer--so someone who works at Honeywell, Rockwell-Collins, Garmin, etc.
If you can access the wiring in the aircraft, especially with the new fly-by-wire stuff, you could cause problems. None of the communications are encrypted (as far as I know), because it's pretty much assumed you can trust what's on the a/c buses. Also, redundancy helps get rid of erroneous data when it only shows up on one bus.
I don't know much about ACARS and ADS-B. While it wouldn't surprise me if there were problems, we also tend to notice rogue transmissions in our spectrum. Much more quickly than people realize.
If you can access the wiring in the aircraft, especially with the new fly-by-wire stuff, you could cause problems. None of the communications are encrypted (as far as I know), because it's pretty much assumed you can trust what's on the a/c buses. Also, redundancy helps get rid of erroneous data when it only shows up on one bus.
I don't know much about ACARS and ADS-B. While it wouldn't surprise me if there were problems, we also tend to notice rogue transmissions in our spectrum. Much more quickly than people realize.