James, my research into the NZAPC is mostly focused on its members who served at Gallipoli, however, I do have some information on the 1917 changes.
When I get a chance on the weekend, I will put something together.
This WW2 picture taken circa 1940 shows a pay and postal officers aboard a troopship.
Pay Corps Two pay and postal officers off duty aboard a 2nd Contingent troopship sailing from Br.jpg
It seems to me that the Pay Corps puggaree was first introduced during WW2.
Pay Corps.jpg