* Nintendo Power Pikachu is an event Pokemon: This specific Pikachu was only obtainable through a special event held by Nintendo Power magazine. It was distributed via a code that needed to be entered on the official Nintendo website.
* Action Replay codes don't replicate events: Action Replay codes are designed to modify the game's data in various ways, but they cannot recreate specific events or unlock content that was only available through limited-time distributions.
* Event Pokemon are often tied to specific game versions: Even if you could use Action Replay to create a Pikachu with the same stats and abilities, it wouldn't have the "Nintendo Power" mark that identifies it as a legitimate event Pokemon.
In summary: You cannot use Action Replay to get a Nintendo Power Pikachu in Pokemon Platinum. You would need to have obtained it during the original event distribution.