Just a quick follow up, I think I’ve solved the problem on my own.
I hooked into the event_tickets_woocommerce_ticket_created action and modified the post meta that sets the ticket number.
function modify_ticket_after_created($attendee_id){
$ticket_id = get_post_meta($attendee_id, '_unique_id', true);
$ticket_id = substr($ticket_id, 0, strrpos($ticket_id, '-'));
update_post_meta($attendee_id,'_unique_id', $ticket_id);
}
add_action('event_tickets_woocommerce_ticket_created', 'modify_ticket_after_created', 10, 1);