Now about how I did it.
1. Downloaded XCOM compatible UDK version: http://www.nexusmods.com/xcom/mods/485 and installed it.
2. Created my own script project:
* Created new folder: Path-To-UDK\Development\Src\XComMod\Classes
* Created new script file: TestMod.uc
3. Created Path-To-UDK\Development\Src\XComGame\Classes and Path-To-UDK\Development\Src\XComStrategyGame\Classes projects to hold dummy XCOM scripts.
4. Created dummy script files (see below).
5. Added newly created projects to Path-To-UDK\Config\DefaultEngine.ini, section UnrealEd.EditorEngine:
6. Compiled and cooked my project. Cooked script package was placed into Path-To-UDK\UDKGame\Script\XComMod.u
7. Renamed XComMod.u to XComMod.upk and copied it to Path-To-XCom-Enemy-Unknown\XEW\XComGame\CookedPCConsole
8. Edited DefaultEngine.ini, section Engine.ScriptPackages:
9. Edited DefaultGame.ini, added a new section:
Since XComGame and XComStrategyGame packages content is cooked into XComMod.u as a set of import objects, those object doesn't have to be fully implemented. We just need a correct package, class, variable and function names.
A class definition, nothing more, as I don't need anything for my simple script.
A copy of decompiled class. It's important, as TestMod class extends XComMod class.
Same as before: only functions, which are actually used. Functions can be empty. Or totally different from original. But they must have the same header and return value.
Empty AddResource function. Again, it doesn't matter as actual game will use actual package with AddResource correctly defined.
I'll write more about XComMod class and how it is used to activate mod scripts later. Stay tuned!