We defined a standard. Well since I made the scripts ill help you.
You say you have a shoot?? well
NPC Code:
setshootparams typeofarrow;
//Your shootstuffhere
if (actionprojectile) {
if (strequals(#p(0),icearrow)) {
//Icearrow stuff here OR IceArrow(); function depends what you want. 
}
}
And you can easily add fire arrows to that, explosive arrows, all kinds
Possibillities = Endless. As long as you have the ideas, that is.