First of all, don't use "udev_random" unless you are certain it is required. It controls how password library generates random sequences (
https://github.com/sjarvela/mollify/wiki/Backend-configuration-options#disable-devurandom-access-no_udev_random). This has nothing to do with enabling/disabling the feature.
Secondly, latest version has this feature enabled by default, so you should not need to enable it explicitly.
But in the end, "enable_change_password" alone should control the feature, and if it does not, perhaps it is in wrong place in configuration.php. It should be in first level in the $CONFIGURATION array.