Restoring a hacked rom?

I was playing Earthbound and decided I wanted to level up a bit faster. By um, setting Mobile Sprout's EXP to say... a billion... and maybe giving the Insane Cultist the Hidden Song... and changing the Death Ray to a Magnum .357... and giving it to everyone... And now whenever I fight a Mobile Sprout I go into an infinite loop of fighting. I tried setting his exp back to a reasonable 100, but whenever I get to Paula's prison.... the game freezes. Any ideas on how I can restore my ROM? To you know, original EB standards.