How do I modify the text in a 'checkout email'?

I sell 16 digit 'Membership Numbers' and have found that the system cannot handle such things as 'normal' numbers [neither can most spreadsheets or databases!] so the system selects a (the next) 8 digit 'code' - the last 8 digits of the 16 required - from a look up list and this is presented as an "Activation Codes:" in the email.
I have modified the wording from "Activation Codes:" to read "Membership Number:" (in /includes/languages/english/extra_definitions/absolute_product_pins.php) BUT I need to 'reconstruct'' my 16 digit code by adding the first (fixed) 8 digits as a text string immediately before the output of the 'code' so the new Subscriber gets the complete 16 digit code string he/she requires.... - still with me? - Help!:dontgetit

Re-reading my first post I see that I didn't express myself as precisely as I'd have liked, hopefully this will be clearer!

I need to 'interrupt the output' or, if at all possible, edit the content of $PRODUCT_DETAIL so that the truncated (last 8 digits) code (stored/delivered as an 'Activation Code') can be restored to the full 16 digit one my subscribers need by my prefixing the first 8 digits I had to strip out (as Zen Cart, or possibly MySQL/pHp cannot handle a 16 digit number as a variable).

I have, of course, been using the 'Developers Tool Kit' extensively while building my store. However, this file (email/email_template_checkout.html) is the one I want to modify but I can only get so far as I cannot find where the defines for the following files are set:

$PRODUCTS_DETAIL
$PRODUCTS_TITLE

they do not produce 'Match Files' in the Tool Kit, all I get is: "Error: No matching Configuration Keys were found ..."

Any help/hints gratefully received! (I have produced a work around for my site (http://www.benefizz.co.uk/join.html) but it's neither as satisfactory or as neat as I'd like.) :huh:

Look in the /includes/classes/order.php file, in the send_order_email() function.
The $PRODUCTS_DETAIL and $PRODUCTS_TITLE are variables built in the html['products_detail'] and html['products_title'] settings respectively.

https://www.zen-cart.com/tutorials/index.php?article=113

Many thanks! :)