Question Materials Atlas question

I have an atlas which has a single material which I want to apply to a specific item. How do I assign that specific part of the atlas to that specific item? Currently there is some auto assignment going on which I cannot figure out how to modify. I have read the manual but cannot locate anything about what you do AFTER creating an atlas.

Similarly, how do I "unpack" an atlas to gain access to the individual materials it contains, or to modify the list of materials it contains?

Thanks In Advance.

 

An Atlas is for combining many textures, not materials. After you create an Atlas, you cant "unpack". so just mod textures and create another Atlas to reflect changes...