WordPress invert post dates

functions.php

<?php
$articles = get_posts(array(
  'post_type'         =>  MY_CUSTOM_POST_TYPE,
  'numberposts'    =>  -1
));

$date = array();

foreach($articles as $art){
  $date[] = array($art->post_date_gmt, $art->post_date);
}

$date_r = array_reverse($date);

foreach($articles as $k => $art){
  //echo 'from: '.$art->post_date.' to: '.$date_r[$k][1].'<br>'; // just to be shure
  $art->post_date = $date_r[$k][1];
  $art->post_date_gmt = $date_r[$k][0];
  //wp_update_post($art); // enable this when you're sure :)
}