Well you can see on the video example above he's working with internal components. I always work with external components, because this is the only way to achieve collaboration and models interchangeability for cross-project use. I keep complaining about it here in every other thread but I don't think Autodesk cares much. External components is the only professional way to handle data. One part number - one CAD model that's used cross-projects.
But for some reason Fusion is developed with primarily internal components in mind. I think historically that's what they started with and added external components support much later. As a result a whole gamut of features that are available for internal components - like the subject of this topic or geometry modifications in assembly context - are not available for external component assemblies. And nobody seems to be in a hurry to fix it even though these are key capabilities expected from any mature CAD.