I’m using Cycles materials on my model and everything is working fine in that regard. However, the “Solid” view (not the in-viewport “Rendered” view!) material, as apparently defined by the “Viewport Material” rollout, doesn’t have any tweakable parameters. Specifically, I’d like to increase and decrease the “Specular” value of the material.
I realize Specular is an imaginary parameter as far as Cycles rendering goes; again, not asking about that. I’m specifically curious if there’s a way to modify the preview/viewport/Solid-shaded material parameters on a Cycles material, other than just the color.
Hopefully, this image removes any ambiguity! 
Thanks!