It is not a matter of hacking the Materia or Kernel.bin.
Without hacking anything, you can apply both attack flags to your character by equipping both a Slash-All and a 4x-cut.
Observe that one wins over the other.
All attack flags are grouped together based on Materia combinations on the character and the engine then decides which to allow and which to eliminate based on which are supposed to override others.
You would need to modify the engine to allow both attack commands on the character (fairly easy) and then to modify it to allow displaying of both attack commands (possibly hard, but possibly easy).
It is probably hard but it may be easy if you can borrow the code from the Throw/Coin command, which I believe is a hard-coded menu item.
After that, since the flags will still be enabled on the character as valid commands, the game engine won’t argue if you send the attack command for one or the other.
L. Spiro