Ok really simple, put you're bad agg in the first slot of you're party.
now put in this gameshark code:
[M] Must Be On
Copy Battled PKMN (Press L+R+Up. Copies PKMN to respective Party Slot)
Once the master code and battle copy code are on, go to grass,water, etc. Where every you
can find a pokemon to fight, once you found one press L+R+Up right befor you send out your pokemon,(it may take a few trys to get it right but it does work) now if done right you should throw out what ever pokemon you are
fighting(if you are fighting a wurmple you will throw out a wurple to fight as) once that
happens just run from fight,open up you're pokemon party and If done right You're bad egg
sould be gone and replaced with what ever pokemon you fought!
I have tested it and it works!
hope that helps =)