No reliable Action Replay code exists to legitimately raise Pokémon above Level 100 in Pokémon Pearl. The game's engine hard-caps experience and level calculations at 100. Attempts to force higher values via memory editing typically result in instability.
These max out current level to 100 or inflate stats temporarily. They do not and cannot extend the cap.
Enjoy Pearl as designed: the Level 100 ceiling is part of what makes team-building strategic. Cheats that promise to break it usually break your save instead.