Slightly off topic.
I played around with the PS2 version included with Street Fighter Anniversary Collection. Here is a patch that nerfs the AI.https://www.youtube.com/watch?v=kKhYVVJ_VMo
I used cheat engine and PS2 Patch Engine to create the patch. Doesn't quite work on real hardware just yet, PS2 Patch Engine doesn't like Master Codes. I have included my code findings regardless, could prove to be useful.
Back on Topic:
So here are some insights:
*US Super Turbo and its variations will at times ignore the selected difficulty option, for example if you set the difficulty at Zero (Easiest), the game will jump to Difficulty 1 and 2 in later matches. This will reflect in the game's ram.
*Much like the above, removing special move charges can be changed via ram and traced back to code via breakpoint. If I remember correctly either the ram counter goes up or down depending on how long you have been charging your attack (Like Sonic Boom or Flying Headbutt).
*I have yet to see any hack that uses old version characters, I imagine if you can select in training mode then it is certainly doable.
What you would need to do to hack HSF2 CPS2:
1. All of this would have to be done using Mame Debugger, which in itself is a bit of a pain to set up as your rom would need to be decrypted.
2. From there you would have to find the ram addresses for things like special moves and your current/next opponent.
3. Then you would have to set a write breakpoint, so when you move on to a new opponent, the game will stop to tell you the new value being written to ram. Then you will have to hex edit that code to change say SSF2T Cammy to World Warrior Chun LI.
4. You will probably have to re-encrypt said rom so it can be played via normal mame emulators, of course mame will complain about the Checksum but launching via command line could work do.
This is a short summation, so I may have left out a few details. Best of luck!