https://wikitech.wikimedia.org/wiki/Increasing_account_creation_threshold
After this, if the event is in less than 72 hours, you should delete the memcache key by using this command. If the deletion is successful, no output will be shown.
mwscript mcc.php --wiki=$wiki > delete $wiki:acctcreate:ip:$ip > exit
But this doesn't match the key format used in Throttler.php
$throttleKey = $this->cache->makeGlobalKey( 'throttler', $this->type, $index, $ipKey, $userKey );