How to add two zones to an existing loop on its own thermostat…

Crispy

IBC 20-125 with Primary/Secondary setup and 4-zone Taco control. One of my four zones, Zone 2, is a little manifold I made for un-mixed cast iron (the others are radiant). I’ve been using one of the three spots on that manifold for a bedroom with cast iron baseboard. I really wasn’t sure what I was going to do in the house so I built in two extra spots on the manifold for future cast iron. Now I have a bathroom with a cute little radiator on one open tap and a spare bedroom with a chunk of iron baseboard on the other open tap. 

Can I convert that manifold to run all three taps on their own Zone Valves? That Zone 2 manifold already has a circulator and of course also fires the system circulator through the Taco. Can I have any one or all three of those new zone valves call for heat on Zone Two and have them talk to the Taco properly?
Thanks in advance for any help, C. 

GroundUp

Expand the ZVC or swap it for a larger one, and add zone valves or actuators to those 3 loops so the same pump will run but only the appropriate loop(s) will open.