I'm working with Simulink with multibodies. I want to run my simulation until a steady state is reached, modify a value, and run it again. How do I do this?

I've got a multi-body simulation of the human spine with scoliosis going. I'm trying to measure what's known as the Cobb angle which is simply the difference in angle between two pre-selected vertebrae. I want to run the simulation with a force applied and return the resulting Cobb angle before changing the force's magnitude, direction and location, and trying again, to run through a few dozen force configurations.

I need to run it until Cobb hits a steady state (to within about 0.1 degrees), report the Cobb angle, change the force and try again, running through it until I can find a minimum Cobb angle among the few dozen configurations tried.

How do I do this?