Let's play with the Meshes
In this tutorial we'll speak about the models of the game, in other words compiledMesh.pak in GothicIII\Data. Unfortunately there isn't any official tool to insert our models in the game but i'll show you the famous renaming method-you'll understand what i mean by reading this tutorial.
First part of "Play with the Meshes" tutorial
Step 1  : Download G3Pak
Step 2  : Run the G3Pak program go "file>open-GothicIII>Data>compiledMesh.pak. I would suggest you to extract only the G3_Items_Weapons_Melee_Swords_O1 (open-GothicIII>Data>compiledMesh.pak>G3_Items_Weapons_Melee_Swords_O1)
Step 3  : In this tutorial we'll change the paladins sword with the katana and the opposite (katana ->paladins sword & paladins sword ->katana)
Step 4  : Press extract selected
Step 5  : A new folder "compiledMesh" which includes other folders in it will be created
Step 6  : First of all let's find the two swords xmsch. There are in the folder called G3_Items_Weapons_Melee_Swords_O1.
Step 7  : Find the files G3_Weapon_1H_Sword_Katana_O1 (the katana model) and the other one G3_Weapon_1H_Sword_Paladin_O1 (the paladin sword) model. We'll work with these two models.
Step 8  : RENAMING METHOD: Name the G3_Weapon_1H_Sword_Katana_O1 to G3_Weapon_1H_Sword_Paladin_O1 and the G3_Weapon_1H_Sword_Paladin_O1 to G3_Weapon_1H_Sword_Katana_O1. It think you understood what we just made.
Step 9  : Run the game. Now the katana will have Paladins sword model and the Paladins sword should have Katana model
Step 10:
Hope it worked. Here are some pics:
Katana is Paladins Sword
Paladins Sword is Katana
One of my friends, spiros_kreta from the WoG forum had a nice idea. To change the models of one handed weapons with two handed weapons!  Changing for example the orcslayer with the Berserk axe model. Then when click to wield an orcslayer you will wild an Berserk axe! Try it yourself, it look pretty good. The method is the same with the katana-paladin sword one.Here are some exciting screenshots: