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Why would you need to extend the Pokedex if you're only using Bug type Pokemon? Wouldn't it make more sense for you to cut down the Dex? Anyway, for extending the Pokedex you can just use PGE (for FR) or Egg's EM expansion.
Yes, just convert the original creator's names to hex, find the start location for the credits, and alter at will.
41D198 is the starting offset for the FR credits
5E5BE3 is the starting offset for the Em credits