There are some constraints assigning model elements as tagged value values. E.g. I can assign classes, activities or use cases as values of tagged values, but it’s not possible to assign operations and attributes. It wold be useful for me - it gives better posibility of profiling UML.
Sorry to keep you waiting. I forgot to tell you that we will support this feature in the coming version - Service Pack 2. At the same time, we will replace the model selection dialog box to make it easier to locate a model to be the tagged value.
This one is available in Service Pack 2 as well. Attached is a sample plugin for you.