I think you would have to edit the file . . .

/includes/languages/english/login.php
Line #18 : define('TEXT_NEW_CUSTOMER_POST_INTRODUCTION_SPLIT', 'Create a Customer Profile with <strong>' . STORE_NAME . '</strong> which allows you to shop faster, track the status of your current orders, review your previous orders and take advantage of our other member\'s benefits.');

you would want to use the Override system of course