I’ve done the hours of research and now provided you with BP nodes that you can use to dynamically rebind keys at runtime for use with your Key Rebinding UMG Menu!
This is specifically for key bindings that you’ve setup using Project Settings → Input.
These are the bindings that work when you right click in BP and can select your action event names that you setup in Project Settings.
These are the same bindings that you use in C++ with SetupInputComponent in your Character class.
PS: my Victory BP Library is a free download, this is not an advertisement but rather a answerhub post to catch people’s searches for “Rebindable Keys” and such and provide you with a immediate and fully functional solution
I spent hours to figure this all out on my own looking in the UE4 C++ code base.