Hello, you cannot postkeyframes in setup mode, but you can copy the bones transforms:
Tools - Spine User Guide: Copy/paste
Because the pose in animate mode is always relative to the one in setup pose, I recommend making a duplicate skeleton, selecting all the bones in animate mode, pressing CTRL+C (in the viewport and not the dopesheet) with the world axis selected, then selecting all the bones in the other skeleton (if you 're not box selecting them, which is the best option, then make sure you select them in the same order) and paste.
The copy skeleton will also be useful to copy paste all the poses in the animation which will surely be wrecked!
