Normally when you can’t get a customization to be picked up, it needs to be customized “one file before”, meaning, you need a custom version of the file that invokes that file.
So in this case you probably need custom versions of these vardefs:
/var/www/html/modules/AOS_Quotes/vardefs.php:346: 'include' => 'modules/AOS_Products_Quotes/Line_Items.php'
/var/www/html/modules/AOS_Quotes/vardefs.php:555: 'include' => 'modules/AOS_Products_Quotes/Line_Items.php'
/var/www/html/modules/AOS_Contracts/vardefs.php:420: 'include' => 'modules/AOS_Products_Quotes/Line_Items.php'
/var/www/html/modules/AOS_Contracts/vardefs.php:627: 'include' => 'modules/AOS_Products_Quotes/Line_Items.php'
/var/www/html/modules/AOS_Invoices/vardefs.php:256: 'include' => 'modules/AOS_Products_Quotes/Line_Items.php'
/var/www/html/modules/AOS_Invoices/vardefs.php:463: 'include' => 'modules/AOS_Products_Quotes/Line_Items.php'
Although maybe this mechanism could be improved - if we can find where these vardef “includes” are being evaluated, we could add a check for custom files there…