Where would I put a custom defintions file?

[alicia1234]

I guess I am looking for the equivalent of includes/extra_datafiles where I can put some constant definitions and be assured that they would automatically load for every page.

Here's what I tried to do:

I created "my_definitions.php" and put it in includes/extra_datafiles.

I modelled it after the "media_manager.php" file that was already there. My file contains one define statement:

define('MM_EMAIL_TEXT_STATUS_UPDATED', ' <br />Hey! Just wanted to let you know that we\'re working to get your order out as quickly as we possibly can. We\'ve just updated your order status!');

Then, in email/email_template_order_status.html, I added:

<div>$MM_EMAIL_TEXT_STATUS_UPDATED</div>

However, the email displays this:
$MM_EMAIL_TEXT_STATUS_UPDATED
instead of what I defined it to be.

I am trying to do this because what I really want to change is "EMAIL_TEXT_STATUS_UPDATED" but that definition is found in

admin/includes/languages/english/orders.php

and to the best of my knowledge, that is a "core" file that cannot be overridden.