BUTTONS vs THEMES

I’m having problem understanding how the buttons created in: LAYOUT -> CSS BUTTONS relate with themes created in LAYOUT -> APPLICATION THEMES. Anybody got this managed ?
My problem is that I have a theme ABC1 and buttons set called ABC2. When creating new App I want the ABC2 buttons assigned automaticaly to the App. At this moment I can change it in Layout -> Settings but when I need to change those in 300+ Apps it would become a nightmare!
The TOOLS -> Epress Edit is nice to mass update but it does not have a feature to update buttons, so how can I have a default button set defined the way I want ???

But did you assigned this button layout in your theme? (advanced mode)

Thank you for replying.
That’s where I’m having problem with, can you tell me where is it ?