okey this will be probably for that system you linked:
you dont have to do anything with the trackables. If you go to object editor you will see Custom objectives. Now you have to take look on Clarity Potion, Clawns of attack( probably the author miswritten xD ) etc. Create new destructables based on those, just do a minor change: Art - Replaceable Texure File - Change to your button!
Note: Dont forget Destructable ID
If you have done now comes vJass. Without reading apies you will probably not able to use it. Open Trigger Editor!
Go to Testing directory -> Items trigger. I'll do a shortcut now: For your items icon do:
JASS:
//Prew Actions
set ci.dest = 'your' // Between the 's is the destructable ID I said to not forget. That destructable contains the texture, and needs here to use
//Following actions
That you want if you do custom way:
Have a trackable model that is completely invisible square. Trackables must be set up at every place. Like a mosaic
Add triggers, I wont make them for you...
Have a square model that is replaceable texture
The method is the same: Create destructables, set replaceable texture
So when the unit picks up the item create a destructable( ofc to that position which is good for your UI ) with the correct ID, and when drops item destroy it. Thats how that system works.
Not the easiest tutorial but probably theres no one... ^^