about l2decrypt, here's a reply given in acis forums from spirit517, including the image for better understanding
For thouse who want to do the same, now i try to explain how exactly to do that:
1. You take ogirinal .utx and use L2Decrypter.exe (drag and drop). I creates name.decrypted.utx.
2. Next use L2Tool.exe on the decrypted .utx. Here is image tutorial by SweeTs for this step. http://img139.imageshack.us/img139/369/25350351ji4.gif
3. Now you can open this utx in UnrealED and do your changes. (delete original and import new .tga edited in photoshop, gymp or other.)
NOTE: When you importing new .tga via UnrealED (File->Import...) use right compression (DXT1/2/3). Simply check (in UnrealED, written right next to the name) the compression of .tga you are replacing and do the same when you´r importing new one.
4. Save your edited utx. (File->Save...)
5. Now tkae that and drag and drop to L2Decrypter again. It automaticly recognizes that utx is decrypted and encrypt it in 121 crypting type.
6. Now you done. Just pase this utx with right name into systexture folder and that´s it.
NOTE: When you later want to edit that texture again, you do not need L2Tool it again. Jus decrypt and that encrypt via L2decrypter