Sorry, I may have to take issue with this response. Actually, he very well may have to serve CSSD with the modification, depending on a couple of things, mainly... who started the case? In the case where someone goes to CSSD and opens a case with them to collect CS, the parties to the action are CSSD vs. NCP (or paying parent). The collecting parent is added to the case post judgment as a courtesy AND because the system needs to correlate parent with NCP, but if the case still remains CSSD v. (YolandaNewells's Stupid Ex) then yes, CSSD MUST be served with a copy of the modification.