cubicweb #1437082 redefine relation definition permission [rejected]

there is no obvious way to redefine a relation definition permission

using get_relation is forbidden with a "can't use get_relation for relation with multiple definitions"

using:

class my_createde_by(RelationDefinition):
    name = 'created_by'
    subject = 'Case'
    object = 'CWUser'
    __permissions__ = {'read': ('users', 'managers'),
                       'add': ('users', 'managers'),
                       'delete': ('users', 'managers')}

is forbidden with a yams._exceptions.BadSchemaDefinition: conflicting values {'read': ('users', 'managers'), 'add': ('users', 'managers'), 'delete': ('users', 'managers')}/{'read': ('managers', 'users', 'guests'), 'add': ('managers',), 'delete': ('managers',)} for property __permissions__ of relation 'created_by'