I'm not too sure about 'Instant Codes' myself but the other options under 'Cheat Switch' are pretty obvious
Off = regardless of whatever
cheats have been selected - they are NOT in use in game
On/Off[Sel+] = This option allows you to turn On or Off the
cheats you have selected from within the game itself
The button combinations are
Press 'Left' on the + button while pressing the 'Select' button =
Cheats On
Press 'Right' on the + button while pressing the 'Select' button = Cheats Off
Always On = Obvious - the cheats are always On
Under 'Soft-Reset / Realtime Save Switch'
Off = No Softreset or Real time save is avaliable
SR: LR+ABX = Softreset will happen if you press Left & Right shoulder button, along with [A]
and [X] at the same time
SR: LR+ABY = Softreset will happen if you press Left & Right shoulder button, along with [A] and [Y] at the same time
RTS: LR+Select = Real time save is allowed when you press Left & right Shoulder buttons & [Select] at the same time
RTS: LR+Y = Real time save is allowed when you press Left & right Shoulder buttons & [Y] at the same time
NB: you can't have Softreset AND Real time save on at the same time