If your character has joined a new group, and you already have a character bio, you can add that bio to an extra group simply by adding a second tag to your character's file. Multiple tags are separated by spaces. Eg if your character is a member of group 1 and group 2 they would have the tags "characters.bio.group1 characters.bio.group2".

Characters can belong to as many groups as you wish. Simply add a the appropriate tag for every group you wish your character bio to belong to.