Sigh… a friendly soul told me that what I apparently really wanted to do is to create a new child class, and that can only be done with the following C++:
And similarly, my plan to get the editor to pop up/show some form of folder selection can apparently also only be done in C++:
So, leaving the above answers for those who use C++, but I apparently have to continue to do cumbersome stuff manually if I want to stick to Blueprint only. 