As I said before, I didn’t. Can I? Sure! Will it break the game since the scenarios are not designed with them in mind and some of them have overflow problems? Probably.
But I could do an experimental version with skills in the future separated from the main hack.
I know you’re new on this. Don’t worry. Always apply the patch to a unmodified game, always use the original. Then to keep your progress, have the .sav (or .srm, it depends in the emulator) have the same name as the patched game.
As an example, if your patched game is “FESacredHouses.gba” then your save file should be “FESacredHouses.sav”. When I tested the game I did it that way, so I could continue testing from the point I solved a bug or an error.