The PCB diagram only contains a node: PCB_PhysicalComponent. So you can only extend this node.
So it will not be possible to extend it the same way as you did in the QualityAssessment viewpoint tutorial.
I see two simple ways to do this: you extend the existing PCB node with a bordered node containing your QualityAssessment information or you add a new container and you add a link to the PCB node.
The first one is quite straightforward. For the second one you can inspire yourself from the BasicMass viewpoint for example.
If you really want to have the same look and behavior (container based) then even defining a new container will not be good because you will have two mapping for each component and thus two representations for each component.
Another solution is to create a new diagram and to inspire from the one from Capella and change the node to a container. You will probably have to replicate some capella code.