ACARS MU switches automatically between the VHF and SATCOM. Indeed the pilot can change VHF3 from DATA (default settings) to VOICE. But ACARS MU would then switch to SATCOM which there is no reference to a switch in cockpit to turn that off. At least I haven't found one
B777 ACARS can communicate on text basis with ATC. Pilots can transmitt/confirm/receive messages trough ACARS ATC. This in case that there is a voice failure.
ACARS of the B777 is highly sophisticated. It is much more than a dummy text transmission tool.
Martin M... check FCOM 5.40.98
You can deselect ACARS satellite transmissions on the ACARS Manager page of the COMM>MANAGER menu of the MFD. A simple mouse click, but there should be no reason to do so unless they misread the bulletin about loss of VHF Datalink on BP V15... which is digressing as no relevance and only confusing this thread.
Also, an in-flight DATALINK reset should not reset OMS and EICAS maint downlinks.