As you have found,
@StephenT, you can specify a nonzero wind value for a specific airport and save a custom version of that airport so that it persists. That does require making custom versions of each airport where you want to fly.
The method
@Flapper described where you can add the console command to your RealFlight startup script will work for the first airport loaded on RealFlight startup. It will not persist after changing to a different airport, though.
Which method works best for you probably depends on how you use RealFlight most of the time. There is not a way to specify wind speed for all airports at once.
I believe you're pressing the up arrow key instead of the "Page Up" or "Pg Up" key (depending on your keyboard). The up arrow key is "Quick Look at Windsock", and will look at the sock for as long as you hold it, while "Page Up" will increment average wind speed once per press or can be held down for larger, more rapid changes.
It is also worth noting that some keyboards--usually on laptops--share the Page Up/Down functionality with other keys, requiring you to toggle some other keyboard mode before the Page Up/Down keys will work as desired.