For any mesh supporting the parameter sideOrientation, we can now pass two extra parameters frontUVs and backUVs both Vector4. These values are taken in account only for double-sided meshes.
They allow to declare what part of the image to crop and stick respectively on the mesh front and back faces.
// set the rectangle coordinates (u0,v0) and (u1,v1) from where to crop the image as a Vector4(u0,v0,u1,v1)
var f = new BABYLON.Vector4(0,0, 0.5, 1); // front image = half the whole image