I think you misunderstand that VarAC is an application that runs on top of VARA HF, VARA FM, or even VARA SAT. I concur with WD4KAV that to use the same radio as VARA, you'd have to shut off VARA, load the other application, and then switch back and forth. Or, I suppose they could be run in parallel, but that's a lot of work to manage two applications that both want to have access to the radio.