don't believe it!!
Well, how do the mod makers do????
They are mixturing with the files in the patch_d2.mpq file!
From the creator of the Poweritem mod (it's in the readme file):
"For those of you who do wish to view the modded .txt files, they are in the patch file, and there are only three that I modded myself: TreasureClassEx.txt, UniqueItems.txt and cubemain.txt."
I think that is a hint that it's accessible, don't you think?