templates.post.php - new option to top?

We want to add an option to the product block, but instead of editing the original templates.php file, we want to use the my_changes templates.post.php

It works indeed but we want the new option field to be on top of all others, not on bottom.

How to do that ?

Our templates.post.php of my_changes addon:

$schema ['blocks/products/products_scroller.tpl']['settings']['custom_option'] = array (
'type' => 'picker',
'picker' => 'pickers/categories/picker.tpl',
'picker_params' => array (
'multiple' => false,
'use_keys' => 'N',
'status' => 'A',

return $schema;

It successfully adds this option field to the block, but on most bottom, because the array gets updated after.

We need it to be on most top, anyone knows how ?