public class CustomDirtyStateEditorSupport extends DirtyStateEditorSupport
{
  @Override
  public void announceDirtyState(XtextResource resource)
  {
    super.announceDirtyState(resource);
    // update the modified state of the resource
    resource.setModified(isDirty());
  }

}

  @Check
  public void myCheck(MyType p)
  {
      if (!p.eResource().isModified() && ...)
            error(...);
  }