Ability question (easy, i think...)

Pretend slot 1 is the bottom-left ability slot, and each one to the right is one higher. the bottom-right slot is slot 4.

Here's the deal... I want to use triggers to replace one ability (Called ES) with another ability (Called Mental). However, ES is in slot 2, and i want Mental to be in slot 2 when i substitute it in. Right now, i use 'remove ES', followed by 'add Mental', but that pushes the ability in slot 1 into ES's position in slot 2, and then puts Mental in slot 1. Any way to keep Mental in the same slot as ES?

Yes, your abilities have their button position defined in the object editor: it's the "art - button position x" and "art - button position y". y stands for the vertical position of the button and goes from 0 to 2, while x is horizontal and goes from 0 to 3.

x = 2 and y = 1 would mean this:
:\ :\ :\ :\
:\ :\ ^_^ :\
:\ :\ :\ :\

x = 3 and y = 2 is the bottom right corner, where normal war3 heroes have their ultimates.
x = 0 and y = 2 is the position of spells such as frost nova, storm bolt, holy light, mana burn...

make your skills have the same button positions and they should appear in the same place (unless you have them both at once, in that case, one skill gets "pushed" to the first free spot.)

Awesome! Buuut.... I need to be able to set the button X position in a trigger (for reasons specific to my ability system...)

Then you'll just have to create another spell with the correct button position. There is no way to modify button position on the fly.