I didn’t think you could do that either, but I’m sure everyone has their own story and experience with paths. I tried my best to prevent anything from being loaded on my C: drive with Windows, but anytime I reinstalled, it still created an AppData\Roaming\Microsoft Flight Simulator directory (I’m a Steam user).
Everything has worked fine, and it was only like 57 meg, so I didn’t worry too much about it. But I admit I will be curious as to what happens the next time MSFS updates your system. I hope you get to keep it the way it is and that it continues to work for you.