The Copy/Paste/Paste Mirrored buttons are available on the Setup rollout for all body parts. You can copy any body part on a CATRig and then paste it to another of the same type on the same or a different rig. For example, you can paste a copied bone to another bone, but not to a hub.
Click to copy the settings of selected body part ready for pasting. When the copy buffer is empty, or contains data from
a different type of body part, this is the only available button.
Click to apply the settings of the copied body part to the selected body part while mirroring (flipping) the pasted settings.
Modify panel 
Click to apply the settings of the copied body part to the selected body part.