Валентин

RewriteEngine On
RewriteRule ^media/([^/]*)$ /instruction.php?instr=$1 [R=301, L]

if (isset($_GET['utm_source'])){
   $url_add = '?utm_source='.$_GET['utm_source'];
}

else {
  $url_add = false;
}

<a href="http://2example.com/order<?= $url_add?>">Купить</a>

RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /index\.php\ HTTP/
RewriteRule ^index\.php$ https://site.com/ [R=301,L]