He would be grandfathered in and you can “transfer” any type of public pension plan in New York. If you started civil service and was paying into Tier 6, you cannot go back in time and attain Tier 4. The deadline to join Tier 4 was back in 2008.
https://www.city-data.com/forum/new-york-city/2667710-pros-cons-working-civil-service-nyc.html