hanbr on "Modify post meta before inserting new post"

Hi!

I'm trying to modify the post meta before inserting a new post. I can't finda anyway to do this. The closest I get is the wp_insert_post_data filter, but there I think I can only modify the $data array and not the $postarr array where the post meta are located:

add_filter( 'wp_insert_post_data' , 'modify_post_meta_before_insert' , '99', 2 );
function modify_post_meta_before_insert( $data , $postarr )
{
if($data['post_type'] == 'special_post_type') {
// Here I would like to modify $postarr
// $postarr['post_meta_type'] = ...
}
return $data; // Here I can only return $data and not $postarr ?
}