doing something to all units of a specific type at map initialization?

k, I've got a few special effects I want to attach to units, and it's easy to do it for when the unit enters the map....but I want to know how to do it to all units of that type currently on the field when the map begins, without having to make a trigger for each individual unit...basicly I want to clean it up a bit. A lot. I'm sure there's a trigger for it, i'm probably just missing it.

maybe something like;

Unit Group - Pick every unit in (Units of type _______) and do (Special Effect - Create a special effect attached to the wherever of (Picked unit) using Whatever Special Effect)