I think that If you put another object, slightly smaller or slightly bigger than the displace one (I'd go with slightly smaller) with opacity and green color in the diffuse layer it'd be a green glass :) I think the slightly smaller would do better since it would refract it also.
As for the reversing the normal vectors: just flip the normals of the model before you bake the normal map. I don't think it would work as a mirror though.
I suspect that the displace is some kind of screen space shader.
Funny, on a still image it looks more like a mirror/chrome rather than a glass. Maybe add some sort of double-sided object on top of that cube with high opacity but at the same time with high spec value.
Besides that it's great :)
go down with the strength on the displace material.