Unfortunately if you saved the game, you may as well have to delete your save and start over.
I know there's a way to catch mew which isn't so much a glitch but more so a ritual, and I'd just use the missing no method of talking to the old man and swimming on the side of that one island for infinite rare candies.
Other than that, maybe find an emulator that has a cheat engine/system installed for games? Not sure how well game shark works on an emulator.