Each service is defined by a class. The file format they generate must be basically the same as the other services, so that ddrgen can handle it properly. Remember - ddrgen doesn't understand anything about the services, however it will attempt to understand some parts of it so that you can connect.
There is some error handling in that if you have a configuration that appears to be corrupt, DDRHelper will try to recover by giving you a blank file to work with. However this is not always desirable.
In conclusion, when updating a Service class: