Index: tw_tablebuild.inc
===================================================================
--- tw_tablebuild.inc	(revision 2820)
+++ tw_tablebuild.inc	(working copy)
@@ -202,6 +202,15 @@
         );
       }
     }
+
+    // Give modules a chance to alter $tables.  This is hook_tw_relationship_alter().
+    // We cannot use module_invoke() for this, because the table arguments need to be passed by reference.
+    foreach (module_list() as $module) {
+      $function = $module .'_tw_relationship_alter';
+      if (function_exists($function)) {
+        $function($tables[$rawtbl1], $tables[$rawtbl2], $row);
+      }
+    }
   }
 
   return $tables;