Changing cck form field options
I would check a couple of things.


For sanity, make sure that your after_build function is being called by adding a drupal_set_message().
The labels will only change in the Edit form if your values are literally '1', '2' and '3'. Once you save the form, however, drupal will save the original value, not your new label.

function mymodule_after_build($form, &$form_state) {
  $form['field_some_options']['value']['#options'][1] = 'hiyo';
  return $form;
}