Adding a StringProperty with an update callback to a NodeGroup

I was wondering if its possible to add a StringProperty to a node group upper level node. I’d like to keep all the behavior in the node group the same, but on a stringproperty update from something like a draw_buttons call, I’d like to use that string to programmatically build a new set of nodes. Is there a way of extending a NodeTree or something to get this to work?