Problem with commerce_checkout_page_info() function
I think you can handle it with hook_form_later, try something like below,
change your condition according to your checkout base name ,
I hope this help you :

/**
 * Implements hook_form_alter().
 */
function yourmodule_form_alter(&amp;$form, &amp;$form_values, $form_id) {
  if($form['checkout_pane']['#value']['base'] == 'checkout_pane_review') {
    $form['submit']['#value']='yourvalue';
  }
}