I would add action at the end of that code before returning the $file after you have made changes to it. Adding the filter here would insure that it is only run on images that you’ve altered the file name of. The filter is
add_action('add_attachment', 'your_function_name_here');
the first thing that your action should do is to remove itself so that it does not run again.
remove_filter('add_attachment', 'your_function_name_here');
For the rest of the action function see this https://wpkraken.io/blog/wordpress-images/, there is a code example at the end for changing the caption and alt text.
