Mod that allows you to downoald textures in the game.
Go to releases and download TextureLoader.dll. Once download, put TextureLoader.dll into MODS/TextureLoader folder in Spaceflight Simulator_Data. You can found Spaceflight Simulator_Data in folder where you install steam in the nex path: Steam\steamapps\common\Spaceflight Simulator\Spaceflight Simulator Game\Spaceflight Simulator_Data. Then launch game and close after loading.
Spaceflight Simulator_Data/TextureLoader/(ColorTextures, ShapeTextures, ShadeTextures) path will create automatically. You can put your textures there. You can downoald References.zip in releases (stock textures in TextureLoader format)