If you installed the assets from the Genshin Characters into UT2004, these files can be put in the System Folder of KFMod20(Or 2.5 and newer) to add Genshin Impact Bots. To enable, you'll have to go into KFMod20.ini (or what the mod folder is called) in the same system folder. Search for "AvailableChars" And put this section in the list and then save:

AvailableChars=Amber
AvailableChars=Charlotte
AvailableChars=Chevreuse
AvailableChars=Furina
AvailableChars=Hu_Tao
AvailableChars=Keqing
AvailableChars=Mona
AvailableChars=Nilou
AvailableChars=Sangonomiya_Kokomi
AvailableChars=Silver_Wolf
AvailableChars=Xiangling
AvailableChars=Yanfei
AvailableChars=Yoimiya

To make the characters available from the selection menu to be playable, you would have to edit KFMod.u under "KFGameType" and change "AvailableChars" there. But it is a much bigger hassle.