Conflating Graphs in GraphViz

GraphViz remains the major leading competitor to sliced bread, but I'm confused by the two web sites and the two versions extant, and reference to stream filters.

3. in my applications, the biggest challenge is fitting data onto the screen, when I have a bunch of "functionally equivalent" nodes lining up with each other. (Below, I've color-coded four obvious clumps of functionally equivalent nodes below.) I'd like to replace all yellows with one big yellow containing all the labels from the ancestral yellows, all greens with one big green, etc. That is, conflate all nodes with identical inputs and outputs into a single supernode, and put the labels for all of the constituent nodes into the supernode. There would be no loss of information and a big gain in simplification (indeed, the colors are just expositional crutches. the solution would make them unnecessary).