For a long time, a Visual Studio/MSBuild extension named Slow Cheetah as helped to transform application configuration files. It is certainly a recommended Task in any .Net DevOps environment.
While many had hoped that the transformation capabilities would be native to Visual Studio 2017, Microsoft has instead "adopted" the Slow Cheetah extension and has released it from the Microsoft GitHub account.
The biggest news -- it now supports JSON transformation using the new JDT schema.
Recommended!