I'm trying to get into modding the game. From what I've read here, I understood I can just unpack pk3 files, and the game will use files from the unpacked folders first? I did unpack 0ufos.pk3 to tweak some weapons, costs, etc. This worked quite well, the game accepts my changes just fine.
However, now I want to test some gfx changes, and added a new main menu screen. I unpacked 0pics.pk3. Then I placed my own main_bg.png under \UFOAI-2.5-dev\base\0pics\pics\background\ (overwriting the original)
But my new file does not show up in game, only the standard screen with the greenish earth.
I also tried to move the whole background folder incl. new gfx into a newly made mods/mymod folder, then launching the game with the suggested parameters to load "mymod", but I always get the green earth menu. How can I tell the game to use my gfx instead?