theme-settings.php

<?php
/**
 * @file
 * Default theme settings.
 */

/**
 * Add toogle option to theme settings to enable/disable dropdown menu.
 */
function ec_resp_form_system_theme_settings_alter(&$form, &$form_state) {
  $form['dropdown_fieldset'] = array(
    '#type' => 'fieldset',
    '#title' => t('Dropdown menu settings'),
  );

  $form['dropdown_fieldset']['disable_dropdown_menu'] = array(
    '#type' => 'checkbox',
    '#title' => t('Disable dropdown menu'),
    '#default_value' => theme_get_setting('disable_dropdown_menu'),
  );

  $form['interinstitutional_fieldset'] = array(
    '#type' => 'fieldset',
    '#title' => t('Interinstitutional theme'),
  );

  $form['interinstitutional_fieldset']['enable_interinstitutional_theme'] = array(
    '#type' => 'checkbox',
    '#title' => t('Enable Interinstitutional theme'),
    '#default_value' => theme_get_setting('enable_interinstitutional_theme'),
  );

  $form['#submit'][] = 'ec_resp_theme_settings_submit';
}

/**
 * Form submission handler for ec_resp_form_system_theme_settings_alter().
 */
function ec_resp_theme_settings_submit($form, &$form_state) {
  // The 'easy_breadcrumb-segments_separator' variable is used by
  // easy-breadcrumb module, to construct link separators.
  // For interinstituional template, we replace it by an image.
  $separator = ($form_state['values']['enable_interinstitutional_theme'] == 0) ? '>' : ' ';
  variable_set('easy_breadcrumb-segments_separator', $separator);
}