Currently, Gridsync declares certain default application configuration values -- like the application's name, signing identity, help URLs, default connection/grid, feature flags, etc. -- in gridsync/resources/config.txt. This is intended to provide a centralized means for developers to modify certain aspects/behaviors of the application in its "frozen" state (i.e., without the need to "recompile" the application with PyInstaller) but which may not be appropriate to expose to end-users (e.g., in the "Preferences" dialog). Nevertheless, modifying the config.txt file (and/or maintaining different config.txt files for different purposes) can be a burdensome exercise (particularly on GNU/Linux, where the AppImage would need to be extracted or mounted separately in order to modify config.txt). Accordingly, it would be preferable if these configuration values could be overridden more easily by developers and/or testers at runtime (i.e., without the need to modify the application package itself) -- perhaps via environment variables.