One way to do it is like this:
Step 1)
Go into FPS \Files\skybank\
Step 2)
Go into the folder of the skybox you want for the test mode
Step 3)
Copy all (don't cut, COPY) of the files in the folder (the .dds textures & the .x file)
Step 4)
Go into the \Files\skybank\ww2\Gas (Default skybox, for me anyways) folder and create a new folder called gas_backup
Step 5)
Move all of the current files into /gas_backup/
Step 6)
Paste the files you copied into the Gas folder, and rename each of then from, for example "war_B.dds" or "war.x" to "gas_B.dds" or "gas.x"
Step 7
Open up gas.x in wordpad, hit "edit" then "replace":
- In the "Find what" box, type in the name of the skybox you copied from... for example, "war"
- In the "replace with" box, type in "gas"
Hit "Replace" all, save the .x file and it should work just fine.
Hope this helps. I copied this along time ago when I needed help.
mk83 Productions