Unity Prefab Variant Tip
Editing the rig of a Blender file breaks regular prefabs that use it (this was a long-standing issue that was never fixed). As far as I know, this problem only happens in Blender since its FBX exporter is limited compared to Autodesk products like Maya and 3dsmax.
The new Prefab Variant feature effectively solves this issue because variants keep the "connection" to the fbx file intact. This works because Unity treats blend/fbx files as prefabs themselves.