Open Security Role Manager, then with your custom role selected, go to View: Policies. Expand Policies to the policy in your screenshot, and ensure that the role has 'Apply to Resource Targets' checked. I imagine it will require write access as well, so ensure Write access is checked under System Permissions. IF you ensure Write access is checked and Apply to Resource Targets is checked, save changes, and reload the page with the custom role, does the target appear editable?