Disable / readonly for relationships field

[cfab]

Not sure why, But I can't disable or make readonly a relationship field with for example this:

 ->addRelationship('state_parties', [
                'label' => 'State parties',
                'instructions' => 'The state parties to the conflict. Do not touch, it is calculated through the linked conflicts.',
                'post_type' => 'actor',
                'filters' => ['search', 'taxonomy'],
                'readonly' => 1,
                'disabled' => 1,
            ])

Should I just make a text field and store those ids in it, because a text field can be disabled without problem.