Can't change add to cart button value
I've used this code and worked fine:

function MY_MODULE_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if (strstr($form_id, 'commerce_cart_add_to_cart_form')) {
    $form['submit']['#value'] = 'CUSTOM BUTTON VALUE';
    //dpm($form);
  }
}