How to add custom column in-between people/users admin page table?
You need to change the sequence of the array, like:

function meme_user_update_form_user_admin_account_alter(&amp;$form, &amp;$form_state, $form_id) {
  $changed_column = array(
    'data'  =&gt; 'LAST CHANGED',
    'field' =&gt; 'u.changed'
  );
  $operation_column = array_pop($form['accounts']['#header']);

  $form['accounts']['#header']['changed'] = $changed_column;
  $form['accounts']['#header']['operations'] = reset($operation_column);

  foreach ($form['accounts']['#options'] as $key =&gt; $row) {
    $user_object = user_load($key);
    $user_language = ($user_object-&gt;language) ? $user_object-&gt;language : LANGUAGE_NONE;

    $operation_column = array_pop($form['accounts']['#options'][$key]);

    $form['accounts']['#options'][$key]['changed'] = $user_object-&gt;field_user_changed[$user_language][0]['value'];
    $form['accounts']['#options'][$key]['operations']['data'] = reset($operation_column);
  }
}