drupal7_text_format_alter.php

<?php
/**
 * Implements hook_element_info_alter().
 *
 * Sets the text format processor to a custom callback function.
 * This code is taken from the Better Formats module.
 */
function module_element_info_alter(&$type) {
  if (isset($type['text_format']['#process'])) {
    foreach ($type['text_format']['#process'] as &$callback) {
      if ($callback === 'filter_process_format') {
        $callback = 'default_text_format_filter_process_format';
      }
    }
  }
}

/**
 * Callback for MODULENAME_element_info_alter().
 */
function module_text_format_filter_process_format($element) {
  $element = filter_process_format($element);
  // Change input format to "Filtered HTML" for body fields of article nodes
  if ($element['#bundle'] == 'bundle_name' && $element['#field_name'] == 'field_name') {
    $element['format']['format']['#default_value'] = 'format_name';
  }
  return $element;
}
?>