Related product array with user input

I am using woocommerce (but this is a general question regardless) and I am using the following code as the footer of my single-product.php page (I’ve created a “Related Products” section) and I am wondering if there is a way that I can alter it to make it possible for admin to be able to add values from the product admin page; I want certain products to show closer related products instead of totally random ones.

Is there a way I can create a custom field for something like product ID or tag and then add that custom field as the orderby value so those products/tags have a better change of showing up vs. random products?

If not, is there anything else I can do? I am simply looking for a way to allow an admin to choose closer related products to appear.

$args = apply_filters( 'woocommerce_related_products_args', array(
    'post_type'            => 'product',
    'ignore_sticky_posts'  => 1,
    'no_found_rows'        => 1,
    'posts_per_page'       => 5,
    'orderby'              => rand,
    'post__in'             => $related,
    'post__not_in'         => array( $product->id )
) );

Here is my related-footer.php file with the complete code that includes the above snippet.