/**
 * Implements hook_entity_prepare_form().
 */
function {{ machine_name }}_entity_prepare_form(\Drupal\Core\Entity\EntityInterface $entity, $operation, \Drupal\Core\Form\FormStateInterface $form_state) {
  if ($operation == 'edit') {
    $entity->label->value = 'Altered label';
    $form_state->set('label_altered', TRUE);
  }
}