I'm assuming you mean im Fire Red? So changing it so you can select either Grookey, Sobble or Scorbunny instead of the regular gang?
Basically yes, but you would have to either add them first of course, or else replace some existing pokes.
There's a thing called the Dynamic Pokémon Expansion that adds basically every 'mon. It's normally coupled with another thing called the Complete Fire Red Upgrade as well.
Worth looking into if you insist on binary hacking.