I'm not sure how but probably a action replay
An Action Replay/GameShark, the game, and codes.
No.You can learn to hack various video games for pretty much any console, at GameHacking.org (see Related Links below).
to hack different games you need different kinds of tools. You can hack NDS, VBA, and GBC roms. For hacking tools go to the link below: http://wahackpokemon.com/en/download/tools-gba
The easiest way is to use an Action Replay, that you can buy at Wal-Mart, or Gamestop for about 20-25 dollars.