If you look through this page and the next there are some threads about this. If you browse through them you will notice that there is currently a conflict with extracting files and manipulating them as opposed to how easy to was at first to change texture files in MW3 with Pakscape. It is a similar problem as there was with BLOPS2 but not the same problem. In other words it probably isn't impossible but right now there is nothing. I wouldn't put it past people to try though.