- preg_replace: documentation ( source)
<?php
$str = 'Magna adipisicing veniam est amet labore do mollit deserunt esse. Ipsum minim sit [[consectetur qui consequat]] elit id irure. Occaecat magna do voluptate commodo veniam nulla adipisicing.';
$pattern = '~(?: \G (?!\A) | \[\[ (?= [^]]* ]] ) ) \s* \K [^]\s]~x';
$result = preg_replace($pattern, '*', $str);
echo $result;