You can always add a new C++ class extending the appropriated BehaviorTree component that you need later if you need a function to be done in C++. Then rebase the Blueprint to extend from your new C++ class which only adds the functions you need. You don’t need to start with it.
Having the visual editor for BehaviorTrees is an swesome tool. In UE3 I did BehaviorTree’s and imported an xml file which decribed the tree. It’s much easier in a visual editor, especially one that gives you the debugging info where you can see the execution flow in real time instead of just stepping through it in a text editor.