Help with mod？

I've been seeing lots of mods lately like g36e to g36ke and famas to l85a1 mod. I was wondering how to do this? Is it just like copying and pasting the skins of one weapon to the other or does it involve more. I've been reading on how to reskin weapon tutorials and wondering if weapon conversions follow this process. If there is a tutorial on how to do this don't flame and just link me. Thanks.

I wanna mod like Corndog, Davidrc and Mongoose xD

WOW! your not even a choob, and you dont know how to read a tutorial or use the serch button?....

there are like 10 bloody tuts...