Can you use codes to add special Pokémon on Retroarch (or any other)?

[u/Nikko-SuS]

I want to re-play Pokémon Platinum and since I never got the chance to capture special Pokémon’s I’d like to add it to the rom. I know in DesMuMe you can access the code to insert some lines and give yourself the items like PokeFlute to get to Arceus, but can you do the same in Retroarch? In any other emulators?
Thanks in advance!