Super-Admin: Any way to globally enforce a new privacy setting?

Hi - I realised I had my global default privacy set in a way I didn't want (VIEW MY PROFILE was set to REGISTERED ONLY).... So users have been registering accounts and getting that privacy level.... now I've realised my design mistake, I want to change that privacy to EVERYONE.... So I've done that back-end but it doesn't seem to change everyone's - Is there anywhere I can go to mass re-assign a privacy level like this, or is it just not possible?