<?php
add_filter( 'posts_pre_query', 'hi_roy', 10, 2 );
function hi_roy( $return, WP_Query $orignal_object ){
	remove_filter( 'posts_pre_query', __FUNCTION__ );
	$query2 = new WP_Query( [ 'post_type' => 'mantelope' ] );
	$query2->posts[] = get_post(42);
	$query2->found_posts = $query2->found_posts + 1;
	return $query2;
}