Hi Brad, thanks for the quick response! I was actually editing my first post to give an update, but I'll instead do so here:
I was under the impression that the new firmware revision would be displayed automatically on power-up. I thought maybe that auto-loading My Setup was preventing this from occurring, so I disabled this and then re-installed the new firmware, making sure to remove the USB drive after power-down so the "MOUNTING" prompt wouldn't be displayed on power-up. There was still no display of firmware revision on power-up. As you pointed out, my initial assumption was wrong; one must manually check for the new firmware revision via the menu.
The new firmware is now installed, and I have changed the USB MIDI in to Part A. Now I can change registrations on the CT-S500, but play them via a different keyboard!