If you want a Renderer to perform an operation for which there are no Caplin classes, you can easily write you own functionality and use it in a renderer.
Write a class to the interface
exampleApp.exampleBladeSet.exampleBlade.WordReversingFormatter. You would write this class to convert input like "word" into the output "drow". You would also unit-test it (you would unit test it right?).
Include the class name in renderer definitions
RendererFactory instantiates your class when called upon to create a Renderer with your class in it.
<renderer type="exampleApp.exampleBladeSet.exampleBlade.WordReverseRenderer"> ... <downstream> <transform className="exampleApp.exampleBladeSet.exampleBlade.WordReversingFormatter"/> </downstream> ... </renderer>