As for your other questions.
There is not exactly the functionality you describe with disabling the UI. Perhaps you could add a zCache and do an offscreen playblast? Or you could solve the scene in maya command line.
If you want to change multiple properties at once, select the meshes with properties you want to alter. Under the Ziva Tools menu, there is a group of selection tools under 'select connected'. Use that to get the node type you want. Then switch to channel box view (not attribute editor) and any attribute you alter in the channel box will be propagated to all objects currently selected.
For your line of action issue, this sounds like a bug I saw a while back. Are you using Ziva 1.3? Can you reproduce the issue with just a sphere and a curve? Try rebuilding the problematic fiber/lineOfAction setup in Ziva 1.3 if you're on 1.2.
We don't have an API as such. All the MEL commands can be found here:
https://docs.zivadynamics.com/vfx/scripting.html#commands-in-mel
I'll let Lonnie comment on the zBuilder stuff as he's more familiar with that side of things.
Let me know if you need any further clarification on any of that!
Thanks!
Andy