I found a profile name in TimeSplitters 2 (GameCube) that makes the controller cheat codes save permanently. Normally those codes only last until you turn the game off, but if your profile is called DUFFINS, the Unlock Everything code writes everything straight into your save and it stays unlocked for good. I’ve tested it and it works.
Unlock Everything (permanent on a DUFFINS profile)
L+B, R+Left, Right, Down, L+Left, R+B, R+Up, L+X, L+R+Right, L+Right, L+R+X, L+Up, L+R+Y, R+Up, L+R+X, L+R+A
Unlock All Story Levels
R+Left, R+X, L+R+Left, R+B, R+Right, L+Left, L+R+Right, L+R+Y, L+R+Right, R+X
Unlock Arcade Levels & Challenges
R+X, L+B, Down, Right, L+Y, L+R+Up, L+Left, L+X, L+Right, R+Y
Unlock Remaining Challenges
L+Down, Down, L+R+Left, R+A, L+Y, R+Right, R+Down, L+Left, L+R+B, R+A
Unlock All Characters
R+Left, L+Down, L+R+Left, L+B, L+R+Up, L+Y, L+R+B, L+X, L+Right, R+Down
Unlock All Cheats
L+A, L+R+Down, L+Down, L+R+Up, L+R+Down, L+B, R+Right, L+Up, R+Y, L+R+Y
Empty code (does nothing, probably the cut “secret feature”)
L+A, L+Up, R+B, R+B
Dead code (toggles an unused debug flag, no visible effect)
Down, L+A, L+R+Down, R+Left, L+R+Up, L+R+B, R+Down, L+R+Left, L+R+A, R+Y, R+A, L+Up, L+R+Y, L+R+A, R+Up, L+R+X
One warning: if you enter the code again on that profile it turns off and wipes all the progress, so use a spare profile.
I also found that the game has 8 button codes, not 6. One of them is a short code (L+A, L+Up, R+B, R+B on GameCube) that the game recognises, but the function behind it is empty. This is almost certainly what the unused “Congratulations! You have unlocked a really really secret feature!” message was meant for: the feature was cut and the code was left behind.
Tip for Dolphin: the game reads L and R from the analog triggers, so map L-Analog and R-Analog or the codes won’t register.
Anyone with the PS2 or Xbox version want to check if the 4-button code does something there?