Redefine a useless fn key...

Hi, Love your laptops. Really do. But one thing annoys me. The uselessness of fn + F4. You can get the same results (on a windows system) by press windows key + P. Your minimalist design only permits so much on a keyboard, why double up on a function so readily available through windows? It's baffling tbh. So, I'd like to redefine this key so it turns the monitor off instead. Something not so ubiquitous with shortcuts. The power button is set to shut the laptop down so I don't really want to redefine that to turn the monitor off. Perhaps there's something in Synapse that might be of use, but have yet to discover it. Any help on this matter would be greatly appreciated.