* If you understand ResEdit, you can use it to move an icon from one stack to
  another.
*╩An easier method is to use ResCopy, an XCMD available on many
  online services and from user groups.
* The Power Tools stack contains a card that copies resources.
* If you have none of the above, choose the Button tool while inside the
  stack with the icon you want to copy.  Click on the button with that
  icon, and choose Button from the Edit menu.  Go to the stack where you'd
  like to install the button, and choose Button from the Edit menu.  The
  icon resource will be moved along with the button.
  
This article is adapted from the Claris Tech Info database.