1. Do you think using the same four 225/50 will be okay?
2. Are you using run flats? Ever thought about transitioning to non-run flats?
Going to a skinnier tire shouldn't run into any fitment issues, however you'll generally give up some looks and handling. Wider tires have a larger contact patch and give better grip. I can already chirp the tires in a stock QX30, so I wouldn't want to give up any grip, personally. And most people think wider tires look nicer, too.
I do still have the factory run-flats. I am not interested in replacing with non-run-flats. With the lack of a spare tire I wouldn't feel comfortable going to a non-run-flat design. My wife is the primary driver of our QX30, so run-flats give me a little peace of mind that she can get home or at least to safety if she experiences a blow out.
2018 Infiniti QX30 Premium AWD - Majestic White
2019 Volvo XC60 T6 AWD Inscription - Onyx Black Metallic
2009 Kawasaki Concours 14 ABS - Candy Diamond Red
1986 Honda CB700SC Nighthawk S - Candy Aleutian Blue and Shasta White