What I wanted to know -maybe I should have been more specific- is what program is usually used to open the HuCard's program so that one can make the necessary changes to it's data before putting it on a disc.
Since a have a little experience with his, I can share some info. Disassembler for one. A emulator with a decent debugger for two (more important than the disassembler by far). A good level of knowledge (low level) about the PCE system, hucards, and the CD system along with the system cards. Some games can be hacked fairly easy by tracking done a few opcodes and rerouting them to BRK opcodes as a software INT call (it's the minimal amount of hacking method). That assumes the game fits in CD ram. If the game is too large, then it gets rather advanced real quick. You'll need to step through the game and really understand
a lot of the underlying funtionaly, sub routines, structure, etc. Then, if it's possible from the structure/layout, you attempt to brake the game up into levels and assets (which will need to be hacked for new pointer/address locations). And finally adding a hook for when the player 'passes' or such, load from the CD the next build of the game (which is the core game + a different level). You have no source code, so a lot of work is figuring out the games structure/data/routines/logic. The rest is the easier part. There are rom hackers out there that do exactly this kind of work. It takes strong will and a good amount of patience, and a lot of time.
I was one of three that did the translation project of Bubblegum Crash (Dave Shadoff dumped the text, Matt translated it, I did the rom-hacking/compression/print routine/text insertion). I expanded the rom size to fit the replacement text back in, because I had no plans for a conversion to SuperCD. So I didn't care about the rom size per se (went from a 4megabit rom to a 6megabit rom). Though I haven't looked at the game in years, it might be possible to hack it run via SCD and AC memory. The pointers to the text can easily be relocated to AC memory, as well as the font data. But I'm definitely not going to do this. I loved the old Bubblegum Crisis/Crash series (didn't care for the new one/remake), but to be honest... the game isn't that great. So it's not worth my time to do all that work (especially now) when someone could just as easily play it on an emulator or flashcard.
