Inbuilt measure tool - how to access c++ code

Building the engine from source and then changing the FDragTool cpp worked for me.
I now have a different standalone editor than the one that ships with the Epic launcher.

I wish there was a way to change the FDragTool cpp inside an ordinary c++ project opened by the packaged launcher editor. That way i wouldn’t have to maintain a separate editor.

Cheers
b