I realize use of the mute wire for grounding pin2/slot 4 of the harness is simply a convenience - proper connector. A question I've seen asked, but not answered - will relocation of the mute wire effect use of onstar muting via the GMOS-LAN-01 adapter?

no, the module takes car of muting the radio itself. the mute wire is really only needed with 3rd party bluetooth adapters, ie parrot