Setting data inside subtree

[Luminoth]

I haven't yet been able to find an example of how to handle this, if I have a node that's something like this:

@tool
extends BTAction

@export var node_path: NodePath
@export var text = ""

func _generate_name() -> String:
    return "Set Label"

func _tick(_delta: float) -> Status:
    var n: Label = scene_root.get_node_or_null(node_path)
    if is_instance_valid(n):
        n.text = text
        return SUCCESS
    return FAILURE

just real basic has a node and text variables. If I put this in a Subtree, I don't have any way to set the values here from the root tree. Is the general way to solve this to also support looking them up from the Blackboard? Or is there some UX thing I'm missing to be able to set them from the root?