Overriding admin settings form from bootstrap sub theme
You need to create theme-settings.php in your theme directory &amp; add following function in that to add new fields as shown in code below:

&lt;?php
function &lt;THEME_NAME&gt;_form_system_theme_settings_alter(&amp;$form, &amp;$form_state) {
    $form['campaign_pages'] = array(
        '#title' =&gt; t('Campaign Pages'),
        '#type' =&gt; 'textarea',
        '#description' =&gt; t('Specify pages by using their paths. Enter one path per line.'),
        '#default_value' =&gt; theme_get_setting('campaign_pages'),
    );

}


Here theme_get_setting stores the value of your field.