To set these overlay attributes

• In the "Device" section, add the following line (with desired values):

Option "MetaModes" "nvidia-auto-select { 
TegraOverlayBlendmode = PremultSourceAlphaBlend, 
TegraOverlayPriority = 0 }"

Here nvidia-auto-select is the default mode name and can be replaced with the desired mode name.

These properties are per-output and can also be queried/modified during run-time via xrandr.