Hooking content class files

I'm trying to write a hook in to code where the newsletter subscription
is updated. I thought I'd try a hook with

<file name="/includes/content/account/newsletters.php">

but I've found this file never gets modified.
I think this is because /includes/classes/template.php line #167
contains

include('includes/content/' . $group . '/' . $module . '.php');

I tried changing this to
global $lC_Vqmod;
include($lC_Vqmod->modCheck(DIR_FS_CATALOG .'/includes/content/' .
$group . '/' . $module . '.php'));

That allows these files to be hooked by addon modifications