Very work-in-progress.
Back-up any files you try this on and save all other documents. If the script crashes then it will not change back the parameters to original ones.
Since this runs on the same thread as the whole FreeCAD GUI, then it will freeze the whole interface. If the entered Python expressions never finish then you will have to kill FreeCAD.
If it doesn't run because of FEM result is None, then try to run one simulation yourself using the usual CcxSolver tools.
Copy the contents of this repository into your FreeCAD macros directory
(~/.FreeCAD/Macro on Linux).
TODO