As long as your talking about the english versions....
Secret ID Action Replay Codes
Diamond/Pearl:
Platinum:
To Activate: Press the L and R bumpers and open your trainer card. Your money amount has been changed to your secret ID. If your money amount is 4 digits, your secret ID starts with a zero (0).
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As of the other games, I'm not sure. If you like, I can generate you a code to make your secret ID whatever you want. PM me if you want that code.