Hello,
the permalink is there for the following scenario: you want to load a CSS/JS script on a third-party website and you set up a permalink so that, if you deleted the original CSS/JS custom code, then you can recreate another custom CSS/JS code with the same permalink and the third-party website doesn’t have to update their header/footer in order to load the new custom CSS/JS code.
The Simple Custom CSS & JS will automatically load all the custom CSS/JS/HTML codes on your WordPress installation. The naming of the custom code’s file is not of importance, therefore the custom code’s ID is used. For example: if you additionally install a plugin that minimizes or caches you CSS/JS files, then the names of the newly created files are also of no importance and a random string will be used.
That being said, would you please explain the case in which you need the plugin to load the “wp-content/uploads/custom-css-js/custom_footer.css” file on your website instead of “wp-content/uploads/custom-css-js/8103.css?v=4903”?