Hello sparkee,
Unfortunately you can't customize the block yourself, as the scripts that control the data (the data flow Simulink -> Simulink coder <tlc files>) are p-files and not m-files that are editable by you.
I understand your use-case and we'll take it under review for our next update on S32K toolbox that will most probably be live in Q3. I will try to push it as an update to this version (which would be quicker than Q3), but I cannot make any promises.
Kind regards,
Razvan.