you can override the "ReflectionVector" used by the cubemap node. Something along the lines of: So drop down a new Reflection Vector node and use Vector component node to 1-Y. Then plug the results into the cubemap ReflectionVector node.
Hi I using a cube reflection map (dds) in maya 2015 using the standard shader fx cube reflection nodes How can I mirror horizontally my cube map? I tried using mirror u and v in the cubemap node but nothing is visually changing. thanks