This does not remove the coordinate systems from your drawing(dwt). It just removes the association of the True north being repersented on the north arrow and navcube.
The already placed NA's can be reset after you remove the GEO if needed. The Navcube can be turned of in the template file and if you don't use the auto north arrows, no one even knows it is rotated slightly. You cna even set them to remove the north rotation and be straight up, but when you do it rotates the viewport.
I have even cheated and placed the associated NA on a no plot layer and had a plotted NA that is not associated with the viewport. SO one noplot controls the rotation, one is plotted. ANother reason for this is the plotted NA is a custom one, and when I tried for a few minutes to make it a smart one it gave me issues. I'm always pressed for time, it is on th elist to revisit in the future.
I had similar issues trying to use our standard north arrow. It has a north arrow assigned to a rotation parameter. The north arrow rotates inside of a box with text. I like your idea of having the dynamic one on a no-plot layer for a visual notification of a major change in the viewport.
See what happens if you follow this scenario.:
At this point what I'm seeing is that everytime I check the Units and Zone tab and choose OK, the geographic location gets reset. So let's set it then continue without OK.
Can see where the coord system holds and where it doesn't?