Is there a way to only restore permissions and not the content from a SharePoint 2010 back-up?
If yes, how?
that is not possible. What you coud do: * restore the content database to another sitecollection * synchronize the permissions between the two sitecollections with some custom written powershell. I don't think there's an easier way.
You can with some 3rd party tools like Quest Security Explorer. Essentially you would take a backup of the security, and then when needed you could restore it.