How can I use new 12.5 img in a script?

I see 9.xx update has HD images from 10920x1080 but how do I make a script Image value connect for the HD images? What path in script do I set up for it?

Same.
if you have a.png, you must add both a.png and a.12_5.png as image resource.

so I have to make same path twice but name it instead to 12.5?

PPD automatically switches image resolution if exists.
So you don't need to create Image twice.