All resources can be updated in principle. Business rules may prevent that in some cases. In a RESTful space, Tasks would be updated by both placer and filler. In a messaging space, there might be independent task instances. Not clear on what the negative is. Will add language indicating that there will typically be limitations on what sorts of changes are permitted to request artifacts, particularly after fulfillment has been sought. These limitations will come from implementation guides, organizational policy, etc.