I'm using a Moto Z2 Force running Android 7.1.1 with a 128 GB microSD card installed. I wanna upgrade to a 400 GB card. Would I have to re-grant microSD access app permissions for the new card, or do those permissions cover any card inserted into the phone?
The permissions should cover any SD card.
But your phone's max SD size is 256 GB, see http://www.gsmarena.com/motorola_moto_z2_force-8693.php