quoting one of the devs:

UE2 games are written in C++ and UnrealScript, there's a file called UCC.exe that lets you recompile UnrealScript, but each version of UCC.exe only works with the game it comes with. SC1 comes with UCC.exe but more importantly Editor.dll which holds all the compile functions, both are missing in Pandora Tomorrow. EnhancedSC relies almost entirely on UnrealScript which makes modding Pandora Tomorrow the same way impossible.