When you upload your wp-config.php file, the file is stored on the server. Then we read the information and try to process it, to understand each of the values. As soon as we have finished reading the data, the file is automatically deleted.
At any moment the data is stored and will only be available to you when you are configuring the new file. From that moment on you will be able to treat it, change it or improve it and thus generate a new version of the file wp-config.php with new functionalities.