How do I get Unity to update all objects from an .FBX model update?

So I have a 3D model that our art dept created in Blender. We want to be able to have the modelers add "attachment points" inside the model so that they can be very precise and we can access them within our scripts. Let's say that we have a human model and the modelers added an attachment point in the model at the very top of the head so we can add various hats. That hat attachment point is modeled as a child object of the human in blender. We export that model to .FBX and we can import it into Unity (in a models directory). So we then create a prefab out of this model and add a gameobject to the scene of that prefab. The model shows up correctly with a child gameobject for the attachment point...everything works perfectly as we wanted it to.

That's the backstory...here's the problem.

So now we want to update that human model and make the human shorter. So the modeler changes the geometry of the human and moves the hat attachment point lower so that it is right on top of the head again. The model is exported as .FBX with the same name and we copy the model into the Unity asset area (overriding the outdated .FBX model file). We go into Unity and we see that the geometry updates to the shorter human, but the hat attachment point stayed at the taller location.

I looked in Unity in the models area and the model itself that it is importing has the correct child object attachment points. I then go look at the prefab and the model geometry is updated, but the child object attachment point has the old taller attachment point location.

So my question is, how can I get the child objects defined in the .FBX file to properly update the corresponding child objects in the prefab?