I ended up using the sanitize tree function from this post, which seems to allow me to modify the dictionary as I was intending to.
However, the tree's 'selectionData' property doesn't seem to update after the modified data has been applied to the tree. I have to click to a different item and then back to the modified item to see the changes. Is there a way to force the tree component to refresh that property?
In regards to boiling down the issue to send to support, what would I need to do? Make a view with a tree and a button that executes a simple script to change a dictionary in the first level of the tree data?