it is set server side restrictions
even the famous gk mod on warband, the server needed to run it to allow you to spam it
now.. previously there was a way of setting mission templates to spam scream a lot more
but a year or so ago, this game was modded to almost (not quite) hard code the shouts, so even if you spam it, the server wont play it
only way around it is if you run YOUR OWN server with with your own scripts, and remove the timers (can all be found in mission templates), then it will work!