Is it possible to reverse the order of a list of posts pulled from a loop?

Assuming you are refering to the code of this answer

Taking the query from that answer

$args = array( 
  'category_name'  => 'your-category-slug',
  'posts_per_page' => 3,
);

$wpse_235685_query = new WP_Query( $args );

you would then, to reverse the order of your results, need to modify the query $posts object, like so

$temp_posts = $wpse_235685_query->posts;  // store the posts to work with
$wpse_235685_query->posts = array(); // empty the $posts object
$wpse_235685_query->posts = array_reverse($temp_post); // set back the object to use new reverse order

of course this could be simplified by getting rid of the temporary variable like so

$wpse_235685_query->posts = array_reverse( $wpse_235685_query->posts );

This code should go between your if( $wpse_235685_query->have_posts() ) : and your while( $wpse_235685_query->have_posts() ) : so it doesn’t run when the query returns an empty set.