players are spawning with 3 snowballs in their inventory, and I didn't see any config or part of the CS file that you could prevent that with..
That is dafault, thats what Christmas event does. You also dont need a mod to do this just type "xmas.enabled true" in your console.
Also check out "StartUpCommands" mod, it will run the command on server start. So even after a restart it will be CHRISTMAS!