You should add this code to FFTA that I found on gamefas.
Action Replay Code:
Illua (START + UP on the Unit Menu)
921D5022 00000212
94000130 000003B7
B21D5020 00000000
20000005 00000009
20000007 00000001
1000000C 00000009
20000006 00000092
2000000E 0000005D
10000010 0000047A
10000012 00009502
C0000000 000000C6
20000052 000000FF
DC000000 00000001
D1000000 00000000
D2000000 00000000
Directions:
Go to Main Menu, Unit Info, open the Unit Menu for a character you wouldn't mind converting to Illua and hit START + UP.
That character should be converted to Illua, and hopefully not crash the game. (The name and stats change, however, will not be apparent until you target another character and then move back to Illua. Full sprite change is not apparent until you exit the Unit Info and come back in to reload the graphics.)
Functionality:
This hack will change:
Unit name, unit race, unit job, unit sprite, unit primary ability, unit help text
You get access to the Guile skillset and be able to set another Hume sub ability (including Intuition and Piracy)
(It was necessary additionally hack Illua to learn all skills, otherwise you would never be able to get any Guile skills available
That means Illua will have access to all Reactions and Passives...)
Illua will use the Nightshade job's equipment list and movement rate.
Illua will use the original stats of the unit modified.
This is for my own taste. If you want to hack the stats, there are lots of other codes already available.
Limitations (READ THIS):
Illua will crash the game upon using (known so far, there are definitely more):
Opportunity Commands
Parivir skills (and I am guessing other sword swing skills)
Ultima Masher (and I am guessing other bow skills with flashy animations)
Dual Wield
This is because the sprite is lacking the animation for those commands. Need someone to be able to find and replace those animations
Illua cannot change jobs to anything other than Nightshade without further manipulation by Action Replay.
Illua has a casting animation, so she works fine in testing with Guile + Magick subskills.