There is different file system used by RX and original RBR format.
Wallaby is a free program for trackbuilders created by Wally, the founder of Czech RBR plugin. The rule is that if you want to use it, you need to ask him for permission. Nobody will share it, because every trackbuilder promises him not to do this. The problem is that Wally disapeared and nobody has conctact with him since couple months... Official trackbuilders registered by Wally can also use online shadow generating service and they can reserve numbers for new tracks they work on.
Wallaby program allows to export files to original RBR format. There are so few tools to edit (move, delete objects etc.), but there you add driveline, animations, moveables, tapes and different types of collisions. And you make materials there and export a file with ground collisions/physics from there. As far as I know, there is no other exporter which can allow this.
File system used by Wallaby is DirectX. It's still not 100% the same as factory tracks - DirectX can use one (diffuse) layer, while original game used four - diffuse, specular, blending and shadows. In new tracks you can't use water splash nor original snow physics (snow banks).
Wally is a genius and he managed to add shadows to new tracks