I gave this a lot of thought way-back-when and discovered some....problems with it.
#1. Attack IDs are stored sequentially in the KERNEL.BIN (it's just the way I always type it and I've noticed that no one does that either
) and the "Spell Order" only allows for 54 slots in the magic menu. Those last two slots do absolutely nothing. I'm not sure what they're for, tell the truth.
#2. The Magic menu both in and out of battle will have to be extended from 54 to some multiple of 3 (57, 60, 63, etc). I played around with looking for this and the closest I got was in the window.bin, but in the most bizarre turn of events, the value 54 is only used ONCE in the entire 33,312 bytes of the uncompressed window.bin file. Ergo, I don't think the size of the menu is located here. It could be somewhere else, of course. Several references to 18 exist (the number of rows in the magic menu).
#3. The KERNEL.BIN would have to be made larger if the magic menu were to be added on to. This is not a hard feat, but the game's load sequence would have to be edited to accept the enlarged KERNEL.BIN Spell Order section.
#4. Adding more than two spells would mean displacing all the other attacks after it. This isn't difficult, necessarily, but that means re-pointing a LOT of things. Start indexes for all the other menus. Adjusting the Relative Animation Index increment table for account for the displaced Indexes. Re-pointing EVERY limit break for every character. For the PC version at least, as long as the new magics don't displace "Blade Beam shock wave" past 127 this wouldn't be an issue.
#4a. If it did displace further than 127 (eight or more attacks to be added), the KERNEL.BIN would have to be further enlarged to have more than 128 attacks in the attack data section.
#4b. Same "if" as 4a; Several attacks would have to be edited to reflect these changes. Satan Slam, Blade Beam, Choco/Mog, Zantetsuken, etc because they use the "Perform XX attack after condition Y" effect. Each "XX" would have to be changed for these.
#5. The KERNEL.BIN would AGAIN have to be enlarged to hold an extra name/description of the attack. This isn't bad for the PC users, but this means instant no-go for the PSX users as the barely
under 11 block KERNEL.BIN would likely grow too large (153 extra bytes is too large for this file).
The list went on, but those are the main points I couldn't get around.