Some moments ago, Duke4.net member known only as NY00123 has announced that, with the blessing of current rightsholder Devolver Digital, original source codes of the original 1997 version of Shadow Warrior have been released, alongside some extra early builds of the Build engine itself. 

As of this moment, using these pieces of source code in the proper way explained in the associated documentation will result in an exact recreation of versions 1.0, 1.1, 1.2 Shareware or 1.2 Registered of the original game, as they appeared in official releases.

Thanks to @devolverdigital, @3DRealms, @Hendricks266, TerminX (@voidpnt) and Ken Silverman, you can now download the following package consisting of Shadow Warrior sources matching versions 1.0-1.2, a few older Build engine sources, and other files: https://t.co/Atigg2XdrF

— NY00123 (@NY00123) February 6, 2019

For anyone and everyone who wants to do more than just change existing values in their mods, as well as gaming historians and archivists, this is always excellent news. You can find the thread with the download link and documentation here.