Tower abliity question

I'm changing the human guard tower so it fires cold arrows instead of normal arrows. The problem is that when the cold arrows hit a unit the unit doesn't turn blue or slow down. The only way that I know to add this effect is to give the tower the frost attack ability or the cold arrow ability from unit abilities. By doing that though it changes the missle animation and then I have to go back in and edit the abilty which I would like to avoid to save myself some time.

I noticed on this TD map that I played, the guy who made it achieved what I wanted but without having a custom ability on the tower itself. Unfortunately I am not able to open his map to look at it because it say's its missing a trigger. Does anyone know how he changed the attack to freeze/slow down units without using an ability?

You can do it with triggers... but in my opinion that would suck.
Changing the missle graphic of an ability is as easy as it gets.

Edit NeutralAbilityFunc.txt :

// creep cold arrows
[ACcw]
Art=ReplaceableTextures\CommandButtons\BTNColdArrowsOn.blp
Unart=ReplaceableTextures\CommandButtons\BTNColdArrowsOff.blp
Buttonpos=0,2
Unbuttonpos=0,2
Missileart=Abilities\Weapons\ColdArrow\ColdArrowMissile.mdl
Missilearc=0.15
Missilespeed=1500

change the missleart to whatever.

I'm probably better off just making a custom ability then to match what I want. Oh well I thought I could save some time. I really dislike making triggers for units. I appreciate your help.