Not sure if I am misunderstanding something but I cannot change the export origin by setting up ruler. (I am using old CS5 version of PS.)
According to the GitHub page,
The Photoshop ruler origin corresponds to 0,0 in Spine, allowing you to control the position of your skeleton in Spine.
I dragged the ruler to the center of a circle. However, the json output is exactly the same as no ruler setup. Is there another ruler in Photoshop?