PHP: if($sender->hasPermission("plugin.command.burnall") || $sender->getName() === $this->cf->getNested("allowed-players"){} I guess this could work
PurePerms doesn't waste RAM... Most plugins use little memory... Make sure you mean RAM, not performance.
Notice : undefined property Main::$cf http://forums.pocketmine.net/threads/permissions.14179/#post-139713 at line 2.
Then that's the problem of "want". Permission plugins are the way for plugins to understand the "list" of players you want.
Or you could edit the plugin...(if its a plugin's permission and not PM's) by changing default: true to default: false in the plugin.yml file