These code snippets assumes you have Thesis 2.1+ installed and active. Add this code to the custom.php file in your /wp-content/thesis/skins/YOUR-SKIN folder.

1. Change the "Add One" text above the comment box

function comments_intro_add_text() {
return "Make your mark";
}

add_filter('thesis_comments_intro_add','comments_intro_add_text');

2. Change the comment box fields labels

global $thesis;
$thesis->api->strings['name'] = __('Name Text', 'thesis');
$thesis->api->strings['email'] = __('E-mail Text', 'thesis');
$thesis->api->strings['website'] = __('Website Text', 'thesis');
$thesis->api->strings['required'] = __('Required Text', 'thesis');
$thesis->api->strings['comment'] = __('Comment Text', 'thesis');