Hi Scott,
In my experience it doesn’t matter the M70 command is suspending the modal commands. The factory settings are in MM so I didn’t actually give it any thought but haven’t heard of it causing any issues for anyone.
IMO you are better off leaving the machine in metric. Of the 2 machines I’ve owned metric is native. I’ve seen some issues with some software not working properly when saving toolpaths on the FB group and almost always comes back to an metric/imperial issue with the post processor.
Here’s a link to a different thread in here with a bit different version of this with some explanations of what each line is doing.