How did you do it on a 4.6 agent? Just curious. This has never been a guest side configurable option. Even when setting it at the pool level that is just for configuring VRAM not what the actual displays run at. This has always been a client side setting so users can set what they wan't. Since View 4.0 we have always detected the client side configured resolution and display topology and adjusted the VM to match that at connection time.
For a zero client ( Depending on the firmware version ) if you go to the local configuration, then to the Display settings and then set the preferred resolution override. You can set the resolution you want to run at. From that the session will adjust accordingly.
WP