There is no separate "config file" for a data source connection. The data source connection definition is embedded in the .twb file. The .twb file is a text file in an xml format. The data sources are defined in the <datasources> section, located near the beginning of the file. In theory, you could probably devise a way to alter the values in this section to promote a viz from a lower to higher environment. However, this would be risky, and unsupported.
I understand your concerns because we have similar Dev and Prod environments which are isolated from each other, and recently have upgraded our PCI compliance. Promoting from Dev to Prod has at times been challenging.
Are you using Tableau Server? If so, I suggest you consider creating a Tableau Server within your Dev environment (this is allowed with the standard Tableau Server license). Then, you can create and publish a data source to both Dev and Prod Tableau Servers. While the connection path and permissions may be different in each environment, any views that use that data source should be able to be moved from one environment to another by changing only the server of the viz data source from Dev to Prod.
I hope that helps.