When I need to change the thickness after starting to cut the cant, say 4/4 to 6/4 or something else, I lower the blade (not cutting) onto the top of the cant and adjust the sliding scale to the new dimension (or at the end of the cut before changing the blade height adjust the sliding scale). Then I start cutting down at the new thickness. If I end up with a odd thickness I try cut it from the center of the pith.
I'm planning on making a scale for standard framing lumber dimensions with sticky back paper printed from the computer and sticking it on an aluminum strip in place of the standard woodmizer sliding scale.
Dave