I have been trying to do something similar, by getting the Keynote Text Parameter and pushing it to the Description Parameter. I have managed to get it to work for our system in a couple of ways. They both utilise SpringNodes Collector Nodes to gather information from the Keynote Legend.
First option Gathers information from a 3D View and then finds the corresponding Keynote. I have had to add in a List.DropItems node to drop off the fist item in the view list as it won’t write the information to the view categories. I have also had to remove the Empty lists and replace them with “???” or else it will come up with and error. You may find that if you run the dynamo script it may give you some errors in the final node, the good news is it stills adds the parameters, it is just telling you it cannot write to some System Families.
The second method is pushing parameters to all of the categories in the model. I am unable to find a node that will gather all elements in the model, so I have created a large list of nodes to identify the categories in the model, hence the 34 Item lists. Even though this method is not as neat as the first, it will allow information to be pushed to detail components. It seems to work better in our workflow. You may get the same errors as before, but it is also just notifying you it won’t write to some system elements.
Hope this helps.