ACARS
To torture an analogy -
ACARS is like SMS on your phone, and more accurately, its like Apple's iMessage.
The ACARS generates a msg. In then makes a routing choice of which way to send the msg to "base".
The msg then gets sent to the appropriate system for transmission (VHF, HF or Sat, depending on availability).
(Using the iMessage analogy, its sends the message preferably via Wifi, then 3/4G if Wifi isnt available).
So, disabling ACARS stops messages being sent - via VHF/HF/Sat. It doesnt necessarily turn off any of those specific comm sets.
If I wanted to "stealth" a 777, you'd turn off the Transponder and ACARS - they both automatically transmit data. There might be other systems you'd turn off - external lights, dim cabin lights for instance. TCAS if turning "off" the Transponder doesnt also shut that down.
As for VHF or HF, that just requires discipline not to transmit from the flightdeck. You might want to keep them on to monitor ATC.
Sat comm's is interesting. Out of VHF/HF and Sat, its the only one that maintains, in some form, continuous communication with the Sat. Like a cell phone maintains communication with the tower when not making a call.
I can see this being overlooked if, hypothetically, someone wanted to turn a 777 dark.