how to modify / customize a coloramp? New to blender, coming from engineering discipline and want to learn more about rendering CFD/model results in Blender.

Right now I'm struggling with generating a coloramp for a 3d surface. What I've done is made a random 3d surface to test with, and developed a shading node setup to achieve a coloramp based on the geometry of each vertex. My current shading node setup and render looks like this:



Right now it looks fine and what I think it's doing is scaling the min/max z-values of the geometry to cover the entire coloramp.

What I would like to do is clip the colorramp. For example, to have a min value of -5 and a max value of 5. Anything below -5 will be red, anything above 5 green, anything in between interpolated.

I want to achieve this so I can have a constant coloramp/values between frames if my z-values change.

How can I go about doing this?
I'm not sure I follow your second (sub)question, but as far as the first question is concerned:
Node setup

The important node I think is the Map Range node, which will take the Z-component of the geometry as input (set your desired clamp ranges here) and maps them to [0, 1], which the ColorRamp node requires.
Result

In this animation, I am changing From Max in the Map Range node. As you can see, all values above From Max get clipped to the upper limit of the ColorRamp.
Hope this helps.