In MSFS 2020, there is a vast array of free and paid ways to globally improve default assets, like ground textures, taxiway signs, etc.
Example:
https://flightsim.to/file/40348/hayes-simulation-improved-taxi-marks-and-ground-textures,
In 2024, the only global edits are on the MS in-game marketplace, proving that it’s possible. But it is not explicitly mentioned in the SDK documentation that there is a way to globally change default airports. Is this still a feature for developers in MS 24, or is it locked to Marketplace partners?