During a battle press Select 12 times, then choose MANUAL when the prompt appears. To return to normal,  simply reenter the code. 

Up or Down: Move forward or back. 
Left or Right: Rotate left or right 
L1 + Left: Move left 
L1 + Right: Move right 
L1 + Up: Move higher 
L1 + Down: Move lower 
Square: Grapple 
Triangle: Jump 
D-pad + Triangle: Jump in corresponding direction 
X: Fire primary weapon 
Circle: Duck down 
R2 + Triangle: Fire secondary weapon 
R2 + X: Double fire secondary weapon 
R2 + Circle: Triple fire secondary weapon 
R2 + Square: Quadruple fire secondary weapon 
L2: Take control of next friendly OKE

Gameshark codes

Infinite Funds 800df38e05f5  800df38ce0ff 
Always 1st Turn 800df37c0001  800df3800001 
Base 1 Fuel Maxed 801350f8e0ff  801350fa05f5 
Base 2 Fuel Maxed 80135154e0ff  8013515605f5 
Base 3 Fuel Maxed 801351b0e0ff  801351b205f5 
Base 5 Fuel Maxed 80135268e0ff  8013526a05f5 
Base 6 Fuel Maxed 801352c4e0ff  801352c605f5 
All Bases Fuel Maxed 50005c060000  801350f8e0ff  50005c060000  801350fa05f5 
Base 1 Infinite Ammo 801350f4e0ff  801350f605f5 
Base 2 Infinite Ammo 80135150e0ff  8013515205f5 
Base 3 Infinite Ammo 801351ace0ff  801351ae05f5 
Base 4 Infinite Ammo 80135208e0ff  8013520a05f5 
Base 5 Infinite Ammo 80135264e0ff  8013526605f5 
Base 6 Infinite Ammo 801352c0e0ff  801352c205f5 
All Bases Infinite Ammo 50005c060000  801350f4e0ff  50005c060000  801350f605f5 
Infinite Ammo All Units 500020160000  80134b7e270f 
Infinite Fuel All Units 500020160000  80134b80270f