Action Replay + SoulSilver/HeartGold

One of my friends told me that if you use an Action Replay with SoulSilver/HeartGold there's something built into the new games that will simply reset you game. (aka, making "cheating" impossible.) I don't own an Action Replay, but curiosity got the better of me and I was wondering if this was true or not... I've seen codes for them online, why would there be codes if you can't use it? Thanks for your time.