[Help wanted] Trying to re-compile UPK files.

So im remoddeling an texture of an videogame released back in 2008. I wanted to look if it was possible to update textures (Client sided) so i de-compiled UPK (ue3) files which contained the items i edited. Now i reskinned the items and made NM for them. However i dont know how i can imploment them back.

(Is an universal texture and the object or any items are in that folder)

I was wondering how i can turn it back into an UPK file (I dont have the source code of course) Any help would be apriciated. It wouldnt hurt if its an long process to do so since im willing to put alot of time into it.