Retroactively bulk assign all existing nodes with taxonomy terms to their respective workbench_access sections. Useful if you've got a workbench_access scheme based on taxonomy terms that have existed for some time before launching access control.

custom_workbench.module

/**
 * Retroactively bulk assigns all existing nodes w/ taxonomy terms
 * to their respective workbench_access sections.
 */
function custom_workbench_retroactive_assign_all() {
  $active = workbench_access_get_active_tree();
  if (!$active) {
    return;
  }
  $tree = $active['tree'];
  workbench_access_build_tree($tree);
  $options = workbench_access_options($tree, $active['active']);
  if (empty($options)) {
    return;
  }

  foreach ($tree as $tid => $leaf) {
    $nids = array();
    if (is_numeric($tid)) {
      $nids = taxonomy_select_nodes($tid, FALSE, FALSE);
    }

    if (!empty($nids)) {
      workbench_access_mass_update($nids, $tid, $active['access_scheme']);
    }
  }
}