Change post order by category programmatically

Hi all,
I’m really sorry to post here this question but on the main WordPress forum I haven’t got any answer.

Well, my need is to have the posts of some categories ordered by title and other by post date; I’ve created a child theme where the functions.php already contains this script for ordering by title:

/* Function for changing post order */
function modify_query_order( $query ) {
      $query->set( 'orderby', 'title' );
      $query->set( 'order', 'ASC' );
}
add_action( 'pre_get_posts', 'modify_query_order' );

How would you recommend me to modify this function? Do you have a more clever advice for hacking the post order making it “sensible” to the category where the query is being executed?

Thank you in advance,
Nicola