Should you kill them, they will only return, and then they will tell everyone that you are a murderer, and the guard will come for you. Better to attack them with the snow. Most of the guard are humans, and to humans, such things are seen as play, even though you throw the snow as if it were stone. If they seek to discredit you through the guard for assailing them with snowballs, they will be laughed at, and that will further your revenge, will it not?