How to add script right after ?

Fairly certain this is not possible without editing the actual theme header.php file. The function wp_head() does in-fact include other scripts, not sure you get a choice to add a script right above everything else and to be honest I don’t see why you would need too.

Your constraints seem rather strict, I’m curious why you can’t edit the header.php file. It’s not like updating WordPress will overwrite your changes.

File not found.