Anything it can. SATCOM overwater, with HF secondary backup, again overwater, out of VHF range.
Simple to disable through circuit breakers in the cockpit.
AHM is a different system completely.
Who cares about the ACARS? The final engine data report would have been triggered by the gear down event and would have provided some routine engine data. It’s the AHM ping data that tells us where the plane is.