i dont know about you, but my lego figures cant do slashes other than vertical ones, they can only rotate their hands, and arms don't bend
I think, a cool new animation might be good, but you could just clone the sword and make a newone that looks the same but with a new animation.
You would have both swords and you could say to your friend "I bet your sword cant do this" and you slash
the end.
anyways,
As long as it doesnt overwrite the other sword, It might be ok