Originally Posted by superdave144
There is no model subfolder in this directory. /opt/bitnami/apps/xcart/htdocs/var/run/classes/XLite/Module/JRG/Quantity
It sounds as you missed the "<?php" in the first line in that file, so XC5 doesn't consider this as a PHP script and ignores it.
Anyway, I've tried the code on my local installation and I see that overriding the method is not enough. You should also change \XLite\Model\Product::__constructor($data) as the $amount property is initialised with the constant, not with the value returned by the method. So, you should override it in the constructor as well.
Please check the attached custom module - it should work for you.