Well done sir!
I've always wondered if it would be possible to make Mode B with friendly fire disabled as a selectable option.
There's a Game Genie code - LEXNGIZA - that lets you select it, but there's no text shown, the cursor goes in a blank spot. Makes the game that much closer to the Japanese verion.
I had started looking doing at relocalizing the Japanese version and had recreated the font from the new translation from the Kunio / Double Dragon collection, if I can find my patch I could send it your way.
Danger X did some pretty impressive stuff with the Japanese title screen, maybe he have insights on hacking the title screen from the American version.
I'd love to see more River City Ransom / Downtown Neketsu Mogogatari hacks.
I recently poked around the game also, made this https://www.youtube.com/watch?v=o3_bXn1bk_U
which replaces all the palettes of the gang memebers to while as if they were from Nekketsu High and swapped Kunio and Yamada.. and since I used the old hack of 'supernatural abilities' that is floating around as a base,, it's really like playing as Yamada.