Right-click the Layers table on the Chute Faces tabsheet and choose Rotate Layer... to rotate every face in the currently selected layer about an axis and a rotation point, without having to move each vertex by hand.
Click Rotate to apply. The vertices are left with full decimal precision (not rounded), so rotating a layer and then rotating it back by the same angle returns it to its original coordinates exactly.
If the layer has a non-zero belt velocity (Vx, Vy, or Vz in the Layers table), those velocity components are rotated by the same angle as the geometry – so you can set a belt's velocity along one axis (e.g. Vx = 5 m/s) and then rotate the whole layer into its final orientation, rather than having to recompute the velocity vector by hand afterward. A layer with zero velocity is left untouched (there's no direction to rotate).