You can get and set the uvs by using the mesh.getVerticesData and mesh.setVerticesData:
https://playground.babylonjs.com/#AYXLNF#1
I have updated the uvs for the visible faces, I will let you do the same thing for the 3 other faces 
You can get and set the uvs by using the mesh.getVerticesData and mesh.setVerticesData:
https://playground.babylonjs.com/#AYXLNF#1
I have updated the uvs for the visible faces, I will let you do the same thing for the 3 other faces 