group_hidden_role
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This module is an extension to the Group module that allows you to hide group roles from the user interface.
The module adds a 'Hidden role' checkbox on the group role edit form. Roles with 'Hidden role' option enabled will be not displayed in the group member's list of roles and will be removed from the assignable roles list when adding or editing a member.
Assigning a hidden role can only be done in code or by temporarily unchecking the 'Hidden role' option and enabling it again after assignment.