One function from the standalone version of MIDI Guitar 2 (MG2) that doesn’t translate to the plug-in version is the ”Hold instrument, switch to guitar” functionality of the Sustain pedal script.
Here is a solution for Logic Pro. It requires access to two controller inputs; one being the standard sustain pedal sending out CC64 to Logic directly (we are not going through the MIDI Guitar plug-in), and another controller to handle a simple on/off task assignment.
We use Logics scripter for a Channel filter to filter out incoming messages from MIDI guitar for this setup. So what happens is, when we first play something we have a standard guitar sound play through MG2 on the AUDIO track, and also send MIDI to the SOFTWARE track synth we have loaded. And as soon as we press the sustain pedal first, and use the other controller to turn off the incoming MIDI to the software track, we have an indefinitely sounding synth to play over. When it is time to change chord we just press the other controller again to release the hold, allowing for incoming MIDI again. For practical use it is of course best to have some external controllers assigned for both functions. One way to do this is described in the video.