For this example i will be changing 'Drakefist Hammer' to 'Thunderfury' and making it sheath on my back.
Changing the Model
Step 1) Open your favourite Hex Editor (I Use XVI32) and open itemcache.wdb (Located in World of Warcraft\Cache\WDB\enUS\).
Step 2) Search for the weapon you wish to edit. (I search for drakefist Hammer) [ http://img114.imageshack.us/img114/8740/seachbl5.jpg ]
Step 3) You will see that the weapon's name is listed four (4) times, Put your cursor at the last character of the forth (4th) one. [ http://img456.imageshack.us/img456/7928/lastcharlg6.jpg ]
Step 4) Right next to the last character you will see a blank box (00 Hex code). Then 2 boxes with values in them (These are what we want to change)
Step 5) To get the ID of Thunderfury we open items.csv from WoWModelViewer. Search for Thunderfury it should show something like this - 19019,30606,2,7,13,32,5,Thunderfury Blessed Blade of the Windseeker -- We want the 2nd Number (30606).
Step 6) Goto http://www.afineride.com/dechex.html and enter the number we got from Step 5 into the Decimal box provided. This should provied a Hex number in the Hex Box. (As you can see i got 778E) [ http://img184.imageshack.us/img184/3007/hexcodecg6.jpg ]
Step 7) With the hex number you got we need to enter this into out itemcache.wdb file. Goto the 2 values we found in 'Step 4'. It should be 9B9A [ http://img184.imageshack.us/img184/6929/hexorigrh3.jpg ]
Step Change them to 8E77 (As you can see i entered them the number in backwards) and save. [ http://img114.imageshack.us/img114/9055/hexnewva9.jpg ]
My Drakefist hammer is now a Thunderfury. [ http://img520.imageshack.us/img520/9422/edithb2.jpg ]
(Note: Your values will be different then mine if you are changing different weapons)
Changing the Sheath position
(NOTE: You will need to know the Max Durability of the weapon you wish to change.)
Step 1) Open your favourite Hex Editor (I Use XVI32) and open itemcache.wdb (Located in World of Warcraft\Cache\WDB\enUS\).
Step 2) Search for the weapon you wish to edit. (I search for drakefist Hammer) and select the last character of the (4th) weapon name [ http://img456.imageshack.us/img456/7928/lastcharlg6.jpg ]
Step 3) Goto http://www.afineride.com/dechex.html and enter the Max Durability of your weapon (Drakefist's Max is 105) and get the hex value [ http://img184.imageshack.us/img184/9365/hexsitets4.jpg ]
Step 4) My Hex value was '69'. So i search for Hex Value '69' [ http://img114.imageshack.us/img114/7427/searchkr1.jpg ] and here it is found [ http://img114.imageshack.us/img114/8742/foundfy1.jpg ]
Step 5) Count back 20 Squares [ http://img114.imageshack.us/img114/2356/20stepsbz9.jpg ]
Step 6) Edit that value. Drakefist is 03 (Hip) and i want to make it 01 (Back) [ http://img184.imageshack.us/img184/8756/changedse6.jpg ]
Step 7) Save and have fun!
Complete - [ http://img520.imageshack.us/img520/4043/completevx7.jpg ]
good luck!
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I dont have the full list but from what i have tried
01 = Back
03 = Hip
07 = Hidden (Fist Weapon)
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This isn't the best guide and i'm sure there is an easier way using DBC. If you know another method please post it.