k simply put...
you will NOT be able to modify skins, weapons, vehicles, terrain, objects, buildings, ANYTHING. To do so you would have to go to the HQ where the servers are run, open the files on the server, and modify them there. 90% (at least) of the game's content will be SERVER SIDE (meaning it isn't a file on your computer, rather a file on the server that sends you the necessary files while playing) I've played plenty MMOGs and none have had clientside textures. Asherons call for example, you can hack up its .dat file and you'll get a number of things, such as item icons, but you won't get clothing skins, player skins, etc. So no need to worry, even though I haven't heard directly from anyone that there will be no client side texture files, its safe to say I can bet my life on the fact that there won't be