I think, I always made it this way and never have problems.
I do this:
Put my textute In unreal in Dtx3 compression in generate mipmaps, put true on the masked and twosided surface and save it.
After I put it in the Enc and edit it for put the good name for my utx and double click on it for the " enc- ".
Finally I pass it to the l2decrypt for the ".clear" and erease the enc- and .clear for keeping only my "name_of_my_utx.utx"
Put in my systexture and edit with L2 FilesEdit Ct2.3 the armorgrp.dat, save it in 413 (the same as they wrote ont the descript of the file) and try to see it in game like all the other time but... :s.... you know the end of the story :S