Hi Dragan,
Although we can box map in 3 axes to generate new UVWs, UVWXForm is designed to adjust existing mapping so it doesn't quite work that way. In fact, it's basically a version of 3ds Max's UVXForm modifier but in RailClone. What might work for what you propose is a separate node to apply new Box Mapping. Maybe it could be added to the Transform node, or separated out. I'll mention it to Carlos.
Cheers!
Paul