If that's what you want to do then using this check is better:
```php
//config at release time
$wgMoxiTestNodes = [];

//code, it's using the array suggestion to be able to turn this on on more than one host in case
if ( !empty($wgMoxiTestNodes) && in_array($wgMoxiTestNodes, $curr_host)){
//replace MemcacheClient class
}
```

Then when you're ready after release is done, simply change the config and push it out.