Japanese version cheats
The way to get them working seemed slightly different to the English version to me, so I thought I'd post it here in case anyone else has any problems. Don't start giving me shit for trying to be helpful.
Start a new saved game.
Do the first chapter legitimately without any cheats.
Once you're done, and into chapter 2, quit the game.
Start another new game (without cheats still).
Play until the first checkpoint.
Quit out again.
Go to load chapter 1 in level select.
Enable the cheat codes.
Get to the same checkpoint as you did before.
Cheats will still show as active (disable them manually).
Unpause the game.
Turn the cheats back on.
Quit the game.
Click continue from the main menu.
(For some reason the game wouldn't turn the cheats off automatically so I had to do it manually and it worked,
thought I'd post the information here in case anyone else has the same problems.)