Not sure, but I think that using either your shadow mic or a sm57 through the H5 is possible. This is done with the function Multi File (to verify).
You will then need to use the usb interface ot the H5 but you first have to install ASIO drivers dedicated to separated outputs management. You can find it here:
H5 Multi-Track ASIO Driver
Then you will be able to send separate mono H5 output to MG2 (as far as I understand it).
Regardless of this, pay attention to the problems mentioned in this recent post about acoustic guitars:
About Playing acoustic guitar with MG2
Regarding tuning, there are presets but each string can also be tuned separately and saved in a patch.
However, if this is not possible, different notes transform functions exist in midi applications to transpose selected notes globally but this could transform notes that should not be transposed.
So it would be necessary to manually select the notes to be transposed, which can be very tiring.