As application features are the way forward that we want to recommend to capture all kinds of information for the complete traceability, we do not want to associate the existing requirements and specifications to them. You can associate any other existing rules by selecting a feature in the overview page of the Designer Studio, go to Associate Rules tab, click on Add rule button and associate your existing other rules (expect specifications and requirements) manually one by one to the feature. We do not have any facility at this point to associate rules to a selected work item like user story/bug manually from any screen (apart from associating it during creation/check-in of a rule upon user selection) and recommend to capture/associate all such information at a feature level only.
If a user selects any Agile Workbench work item(user story/bug) that is associated with an application feature during the creation or check-in of a rule, a link reference is maintained against it. All these associated rules are correctly shown under that specific feature only currently and do not have any screen to show/map against the work item manually. If there is no feature mapped against the work item selected for creation/check-in, then the rule page will have record of the work item.