What do you mean? You want to make creep Acquisitoin range bigger, lets say 300? Cause that you can do in the gamplay constants? There is also a trigger, Units/Set Acquisitoin range.
*EDIT*
Well, I took a better look at it, and I noticed I didn't really help. You can only adjust the guard distance of creeps, wich are only units owned by Neutral hostil. So, with this trigger you can easly set units Acquisitoin range, owned by you, a computer or creeps. Or only creeps. How? I will explain you.
Go to triggers. Select ''Unit group/Pick Every Unit In Unit Group And Do Action''
Now, lets first change the first value. Its default is ''(Units in (Playable map area))''. You can keep it like this if you want all units Acquisitoin range to be the same, otherwise you have to select it and pick ''(Units In Region Owned By Player)''. Its default is player 1. You can select ''(Player 1)'' and select'' ''(Neutral Hostil)'', or any other player you want.
Now we have >selected< the units from who we wanne change the Acquisitoin range. Now we need to select what action to do. Select ''Action'' and change its value to ''Unit/Set Acquisitoin Range''. Again you get to value's to pick from. One says ''unit''. Change this to ''(Picked Unit)''. You also have ''Range''. Change this to a value from your desire. 300 for exampel.
This should do it.