Using DSL Viewpoints to add an attribute to a Logical Component

In the *.data.vptext file of my Viewpoint, I declared an attribute as follows:
The above viewpoint specification allows me to add a ConfidentialityAssessment object to Logical Components in the project explorer.
Question nr 1: How can I prevent that the end-user adds more than 1 ConfidentialityAssessment objects to a Logical Component.
In the Logical Architecture Blank diagram, I would like the user to be able to assign ConfidentialityAssessment objects to the shown Logical Components. In order to do so, I created a *.diagram.vptext in which I used the ‘New Diagram - Generate Diagrams for all classes’ action. I changed the extended-diagram to LogicalArchitectureBlank and the import to LABLogicalComponent.
This way I succeeded to make the ‘ConfidentialityAssessment’ objects visible in the palette of the LAB diagrams. I’m also able to drag them to the Logical Components.
Questio nr 2: The ConfidentialityAssessment objects in the ‘package browser’ and the ‘ConfidentialityAssessment’ ojects from the palette are not the same… How to solve this? E.g. when I add a ConfidentialityAssessment object to a logical component, the diagram does not show it (and the other way around).
Thanks for your help!