to trap options modifications in WP use the filter called in update_option()
defined in wp-includes/functions.php:376

do_action("update_option_{$option_name}", $oldvalue, $newvalue);

+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|LP opts| LP own page | WP | LP option            | WP option           | Notes                                  |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             | x  | url                  | home                | only if install_type == root           |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | wp_url               | siteurl             |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | mail_from            | admin_email         |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | blogname             | blogname            |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | shortname            | blogname            | sanitize_title(get_option('blogname')  |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | description          | blogdescription     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | copyright_notice     |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | posts_per_page       | posts_per_page      |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | posts_per_rss        | posts_per_rss       |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | lang                 |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       | x           |    | template             |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | approx_sql_timestamp |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | date_format          |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | short_date_format    |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | time_format          |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | short_time_format    |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | archive_label        |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             | x  | charset              | blog_charset        | strtoupper(get_option('blog_charset')) |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | mail_mailer          |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | mail_from            | admin_email         |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | mail_on_comment      |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | allowed_tags         |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | post_prefix          | permalink_structure | *                                      |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | category_prefix      | category_base       | **                                     |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | archives_prefix      | permalink_structure | ***                                    |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | pages_prefix         |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | pages_suffix         |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | search_prefix        |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | author_prefix        |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | tag_prefix           |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
|       |             |    | category_separator   |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | comment_spam_kill    |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+
| i     |             |    | comment_spam_mail    |                     |                                        |
+-------+-------------+----+----------------------+---------------------+----------------------------------------+

*   if (!empty($value)) {
        $value = preg_replace('/%([^%]+)%/', '{$1}', $value);
        $value = $this->removeWPslashes($value);
    }

**  if (empty($value) && get_option('permalink_structure'))
        $value = $this->base[$opt]; // use default
    else
        $value = $this->removeWPslashes($value);

*** // if we have an empty value we are using raw URLs, and this option is useless
    if (!empty($value)) {
        // use post prefix as our base, minus post-specific values
        $links = array(explode('%postname%', $value),
            explode('%post_name%', $value),
            explode('%post_id%', $value));
        $shortest = strlen($value);
        foreach($links as $l)
            $shortest = min($shortest, strlen($l[0]));
        $value = preg_replace('/%([^%]+)%/', '{$1}', substr($value, 0, $shortest));
        $value = $this->removeWPslashes($value);
        // append year & month if they are missing
        if (strpos($value, '{year}') === false)
            $value .= '/{year}';
        if (strpos($value, '{monthnum}') === false)
            $value .= '/{monthnum}';
    }