Skybox in TE / Data / Pak1 / Data / Models / Texture, add that file in that folder and if you play with voullez night must rename skybox.jpg, here to the sky, and close enrregister
For Courttex, open TE / Mods / ITST116 / Data / pak3 / Data / Customcourt for exemple customcourt 63/64/65 (US OPEN) and to replace courttex . This is done, close and enrregister
For Courta01, open TE / Mods / ITST116 / Data / pak3 / Data / Models / Texture / Stadium / add there in the file of the court you want to change and think rename courta01.jpg is Done!
think back all 3 game files you have changed by renaming them with day instead of night, so you can change day and night as you see fit!