Custom Friend Groups
What happens if I rename my friend group?
Friend groups are kept track of by a number, not by their name. So you can rename your friend groups as many times as you want without any changes to who will be able to see your posts set to that particular friend group.
If I no longer want one of my groups, can I "reuse" it by renaming the group and changing its members?
You could, but it wouldn't work how you probably wanted it to. All the members of the new group will be able to read any old posts you previously made to the old group! The proper way to replace a friend group is to delete the group and then add a new group.
What happens when I delete a friend group?
If you only have one friend group selected on a post, say group1, and then delete group1, the post will still be marked as "Custom" security, but without any specific groups being able to read it. Thus it is only readable by the original poster unless you later change the security setting on the post. Friends groups can not be undeleted.
What can I do if I delete a friends group by mistake and want it back?
You will have to make a new friends group with the same name and people in it, and then you must manually re-set the security level on each post that was originally posted to that group. There is no way to automatically recreate a group after you delete it.