This is from the Deus Ex SDK doc that comes with the sdk , it show's you how to generate the UnrealScript source code for deus ex , how to compile any changes and a quick note on running the game with your changes .

Generating File's :

Run UnrealEd from your System directory.
From the Browse combo box (upper right corner of the editor), select Classes.
Click on the Export All button in the lower right corner of the editor. This will generate the entire
UnrealScript source tree for Deus Ex.
Compiling Change's :

Make copies of all .U files you are making changes too , back up the original DeusEx.U file or any .U file your editing .

Open your deusex.ini file found in the Deus Ex System folder , and around line no.35 change CdPath=D:\DeusEx and change it to CdPath=C:\DeusEx . ( Just change the Deus Ex.ini so it say's cdPath=(your hard drive)\DeusEx , not your ROM drive , it needs to be set to you Deus EX folder on your hard drive )
Delete the DeusEx.U files or the package your editing .
From a DOS box , change the directory from \Windows to your DeusEx\System folder , i.e : cd C:\DeusEx\System , after that type "ucc make" . This will automatically regenerate any missing .u files. If you are prompted to rebuild a .h file, answer no.
Running Your Change's :

When you have made your changes you may want to test them out , if so then start deus ex , activate the cheats and then summon your new weapon/item or if not a weapon or item then do what you must to view your changes. Here is an example of what to do if you made a totaly new weapon :

Start a new game , Activate cheats, type summon weaponlaser (weaponname) and then start using it .