Is there anything like a reverse Proofing mode? Somewhere where I can paste in code that I’ve written in Notepad++ and just use Twine to create the game?
I much prefer coding in something like notepad++ and find having to move between passages in the UI just a bit clunky.
There isn’t a “reverse proofing mode,” but what you are describing is Twee. There are command-line tools like TweeGo and Extwee that compile Twee code into Twine 2 HTML.
You can use whatever editor you want with them and many people (including me) use tools like Atom, VS Code, Notepad++, and others.