Okay, I suppose it could be if the JFK/EWR-CCC + nested CCC-JFK/EWR fares (there are probably the same fare filings for JFK and EWR if international) are cheaper than two JFK/EWR-CCC roundtrips (because they are roundtrip fares with min stay requirements). The connecting airports and GUC usage don't really have any bearing. I doubt they would actually go after you, but technically it sounds like it might be a violation.