It worked!!
I used the Batch file idea (Thanks BadMouth) to switch out (copy over) the Demul.ini file, which in turn defines which BIOS Demul will use for the currently loaded game.
I tested this over and over between Crazy Taxi (USA Bios) and Dynamite Baseball '99 (Japanese/Auto Bios). It worked like a champ!!
I set up one game manually for the USA BIOS (Crazy Taxi), played the game briefly, quit, and then re-saved the resulting Demul.ini file as "USABios_Demul.ini". Then set Demul up for "Naomi Auto Bios select" with a game I knew would only run with a Japanese or otherwise non-USA Bios (Dynamite Baseball '99). Copied and pasted that newly created Demul.ini file as "AutoBios_Demul.ini".
Then I created two batch files entitled "GetAutoBios.bat" and "GetUSAbios.bat" to switch out the saved Demul.ini files I had named "AutoBios_Demul.ini" and "USABios_Demul.ini"
These batch files are executed in the AHK file for each Demul game as:
Run, C:\Arcade\Demul\AHK scripts\GetUSABios.bat
Adjust your path in the code above accordingly.
Example code for USA Bios batch file:
@echo off
Copy /Y "C:\Arcade\Demul\Config\USABios_Demul.ini" "C:\Arcade\Demul\Demul.ini"
Keep the quotes shown in the code above. /Y will instantly answer the query "Are you Sure...?"
Anyway, I hope this can help someone else who has the same question or concern.
Now I just have to go through each and every Demul-Naomi game I already have set up for Mala and add the code to the AHK script accordingly.