Example of how to change the order confirmation button text.

functions.php

<?php //Please do not include the opening PHP tag if you already have one.

function tw_ee_button_confirmation_text() {
  return 'View Full Confirmation Receipt';
}
add_filter( 'FHEE__thank_you_page_overview_template__order_conf_button_text', 'tw_ee_button_confirmation_text' );