Things needed to get started:
*Dds Thumbnail Viewer Download (XP & Vista x86 32-bit)
*Mystic Thumbs (Vista x64)
*.dds tool (Used to open .dds and save in PS)
*Python script for unpacking .PAK
*Winrar or 7zip
Ok, So I'm assuming you have all the aforementioned programs and such. Now we are ready to start modding. Your going to first go to C:\Program Files\NcSoft\Aion and find the .pak you would like to extract.
Alright, Now, You have found the .pak file you would like to open? Good, Now your going to click on the .pak and drag it on top of the .bat file downloaded earlier. It will open a cmd prompt, and unzip everything. It will then make a .zip file with the .pak contents in it. I recommend using 7zip because WinRar was giving me some weird errors. As seen in the picture below, That is the .zip I was talking about. Now on to step 3!
So you finaly unpacked the .pak file, And are now left with the .zip. Now your going to right click the now made .zip, And click Extract to Blah blah. It will now make a folder with ALL the contents of the .zip into a folder. Now your going to open the folder and view the goodies inside. Notice they are .dds? Good thing we downloaded the viewer! Now you can just click on the .dds and see a preview of it before you open in PS. Look at the image below to see what I mean. Now onward to step 4!
Ok, Now that you have chosen which .dds you wanna edit. We can start by opening it. Thanks to the plugin we downloaded earlier. Right click the .dd and choose open with... Then PhotoShop. You will now see your image pop up in photoshop. You can continue to edit with the paint brush, Color Replacement tool etc..Go nuts. When your done, Just save and the Nvidia save thingy will pop up. Always save using this setting shown in the picture below. Now we will move on to step5, Which will be repacking the .pak.
Now that you've had your little fun, It's now time to turn your creation back into a .pak file for you to use. Your going to highlight all the files you edited, Then drag them back into the .zip you created earlier.
Now last, But not least, The .zip where you just dragged your files to, Your going to rename from .zip to .pak. MAKE SURE YOU BACK UP YOUR OLD .PAK FIRST! To do this, Rename your default .pak from SoandSo.pak to SoansSo.pak.bak.