Choose "codenames" from the main menu,then choose your custom profile and enter any of the following codes at the "Secret Unlocks" menu. Be sure to choose the "save Codename" option for the codename "Edit" menu after entering any of these codes; if you dont, the code effects will be lost and you'll have to enter it again.

PASSPORT
PARTY	unlock all characters in Multiplayer mode
GAMEROOM	unlock all scenarios in Multiplayer mode
BOOM	unlock
Q LAB	Unlock all gadget and weapon upgrades