Just thought maybe this hook may be useful? So like you can change configuration file without reloading a plugin. 

Why would you need a hook to know when you change your own configuration?

For example user has installed a plugin on a serser. And it would be faster and easier to change stuff in the configuration file, save it and it will automatically load and you don't need to use command line to reload a plugin because values will reload automatically. 
Merged post..
Or maybe there is a way to get know when configuration file waa changed? 

Configuration files are only loaded when the plugin is loaded, not when the file is changed. There is file watcher setup for configuration files.