I'd go to the final battle on Pride Rock and kick some ass. I don't even know on which side I'd be.. I'm such a traitor XD I'd probably distract the hyenas so they wouldn't hear about Scar's betrayal, I'd be interesting how things would turn out.
I would NOT alter the stampede, because it'd be an example on how people can let their ambitions and feelings control them, and it'd be an event that would be remembered until the fall of the Pride Lands. (Unless the lions started thinking it's all folklore and fairy tales

)