DIY patching of OS X system binaries?
You can use XCode - it's in the App Store, and free. https://itunes.apple.com/us/app/xcode/id497799835?mt=12

Download that whole directory, open up the XCode project: configd.xcodeproj

Then, you can build it using XCode.

You'll probably need to turn off the code-signing protections - Security and Privacy panel in System Prefs. Allow Apps downloaded from anywhere. Not sure if Apple has additional protection for system binaries.

Try it on a different drive, or in a VM and see what happens.