Renamed to _forced. The light blinked at varying frequencies for just over a minute. No graphical output during the process. After that time, light was a steady green. Continued leaving it powered on with no controller input for 10 minutes. After that time, I brought up the Mega SG menu and selected Run Cartridge. No change. Powered down, reviewed the filesystem. The update was renamed to [SN]_update.upd. Removed that and created reset.cfg. Reinserted and powered on, this time it powered up to the menu.
Confirmed the version of the firmware reported and was successfully able to play both a Genesis and a Sega CD game.
Thanks for the assistance.