1. Go to 'Administration > Site administration > Plugins > Activity modules > Manage activities'
2. Make sure all the modules are enabled (eye open)
3. Go to a course main page. Turn editing on.
4. Disable the activity chooser dialogue from 'User preferences > Course preferences > Enable activity chooser'
5. Open the dropdown menu to add a resource and select URL
6. Add a URL with whatever settings you want and go back to course
7. Enable the activity chooser dialogue from 'User preferences > Course preferences > Enable activity chooser'
8. Go back to the course and click on 'Add an activity or resource' and make sure URL is present under 'Resources'
9. Edit /mod/url/lib.php. In the function url_supports() replace:

    case FEATURE_MOD_ARCHETYPE:           return MOD_ARCHETYPE_RESOURCE;

with

    case FEATURE_MOD_ARCHETYPE:           return MOD_ARCHETYPE_SYSTEM;

10. Disable the activity chooser dialogue from 'User preferences > Course preferences > Enable activity chooser'
11. Go back to the course and make sure that URL is not listed in either the 'Activity' or 'Resource' dropdown menus
12. Enable the activity chooser dialogue from 'User preferences > Course preferences > Enable activity chooser'
13. Make sure that URL is not listed when clicking on 'Add an activity or resource'
14. Make sure that the previously added URL resource is still visible and editable