This trick exploited a glitch in older Pokémon games, allowing players to duplicate Pokémon or items by transferring them between the PC and their party while manipulating the game's save data. However, Game Freak patched this exploit in later games, including HeartGold and SoulSilver.
While there might be other glitches or exploits in the game, the PC Box Clone trick is not one of them.
It's important to note that using glitches or exploits to obtain an unfair advantage in the game is generally discouraged and can even lead to bans in online gameplay.
If you're looking to get extra Pokémon or items, consider legitimate methods like trading with other players or using the in-game events and features.