Here's why:
* Fusion is not a legitimate mechanic in Pokémon games. Pokémon fusion is a fan-made concept, not an official feature.
* Action Replay codes alter game data. While they can be used for things like unlocking items or changing stats, they wouldn't be able to implement a complex mechanic like fusion that isn't already present in the game.
It is important to note that using Action Replay codes can potentially corrupt your save data and may be against the rules of online play.
If you're interested in fusing Pokémon, you might want to explore fan-made games or mods that allow for this type of mechanic. However, these are usually not official Pokémon games and may not be compatible with the original game.