That will work for the Video Routing module (VRM) under the passenger seat, but will not work for the main UConnect system. Updates for the main system for 2018s and later are distributed only over the air or through a dealer, they never show up on driveuconnect.com. What we need is somebody with inside access who can get the files.Not absolutely sure, but I think you'd be able to get the files, at least, by entering a 2018 VIN...doesn't have to be your VIN, as I found out when I tried getting stuff with a VIN that didn't actually belong to my car.
That said, I don't know whether the software would actually update as it might sense the conflict between software for a 2018 vehicle being installed in a 2017.
All you need to test it is an appropriate 2018 VIN - I'd give you mine, but I've got a 2017.