So with the right radio / software, could you manipulate the ADS-B information that is part of Transponder Mode-S data to initiate a TCAS RA?
I suppose the question is - are there any vulnerabilities in the FMS which allow the FMS to be programmed via ACARS?
If the answer is no, then the attack potential is to retrieve lots of data and send bogus messages and flight plans into it. I would be very surprised if you can send something to an FMS and for that thing to be automatically used / executed without Pilot involvement?