need help to override some tpl

I don't understant how I can override a file like breadcrumb.vars.php ?

function MYSUBTHEME_preprocess_breadcrumb(&$variables) {
  $breadcrumb = &$variables['breadcrumb'];

  // Optionally get rid of the homepage link.
  $show_breadcrumb_home = theme_get_setting('bootstrap_breadcrumb_home');
  if (!$show_breadcrumb_home) {
    array_shift($breadcrumb);
  }

  if (theme_get_setting('bootstrap_breadcrumb_title') && !empty($breadcrumb)) {
    $item = menu_get_item();
    $breadcrumb[] = array(
      // If we are on a non-default tab, use the tab's title.
      'data' => !empty($item['tab_parent']) ? check_plain($item['title']) : decode_entities(drupal_get_title()),
      'class' => array('active'),
    );
  }
}

I have tried to copy it in template.php with my subtheme name instead of 'boostrap_'
I have tried to copy the file in my subtheme / theme folder and I have replaced the name bootstrap with my subtheme name

but nothings works :(