For copying, you can copy top-level annotations from one group to another through the Hypothesis API. There's a 3rd-party tool for copying Hypothesis data that allows you to easily replicate top-level annotations. [Note: Since we don't control this tool we are unable to provide troubleshooting or support beyond these basic instructions.]
To copy your Hypothesis annotations, go to https://jonudell.info/h/CopyAnnotations/
and enter your Hypothesis username and API token. The instructions to use Copy can be found at the bottom of the page.
For changing the privacy of existing annotations, generally you need to do that by editing each annotation and changing it from "Only Me" to be visible in the group. If you're comfortable using our API
you can probably find a way to automate it.