Dear Alessandro,
First of all, thanks for your search before posting your question.
Indeed, there is no core CB functionality to allow a user B from a group GB to edit a field on the user profile from another user A from another group GA. Only CB Moderators can do this, but then for all profile fields.
I have also checked CB Core Fields Ajax that can allow a Joomla ACL group to edit a field from all users in the profile with Ajax, but it requires also profile edit permissions.
www.joomlapolis.com/addons/cb-core-fields-ajax
And ACL edit permissions are not per profile field nor per tab, but only for all profile fields.
I don't have a solution for this out of the box, without quite some coding, but I have added a FR tracker item so that we can discuss this in the CB Team:
forge.joomlapolis.com/issues/8085
So short answer: don't think it's possible at this stage without some coding.
Long answer: you could probably use CB Auto-Actions to modify with some of PHP code the behavior of the "points field" or "rating field", but such a development is out of scope of our forum support.
Leaving this thread open, maybe a better idea pops up in the next days, maybe from another community member, or from another CB Team member... ?