dben

You should do something like this:

// read custom field
$customFieldValue = get_post_meta( $post_id, $key );

// apply regular expression
// you can set 'content' or 'title' in type argument to select which
// expressions to apply (see options in WP admin)
$customFieldValue = apply_regex_option($customFieldValue, 'content', '01');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '02');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '03');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '04');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '05');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '06');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '07');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '08');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '09');
$customFieldValue = apply_regex_option($customFieldValue, 'content', '10');

// save custom field
add_post_meta($post_id, $meta_key, $meta_value);

You need to add text replace code in simple-text-replace_hooks.php.

As you can see, by now only post content is replaced:

$post['post_content'] = apply_regex_option($post['post_content'], 'content', '01');

Let me know if you need more help

daniele