To clarify cause some of you are too lazy to try.
Class 1 has AK47/GOLD CAMO
Perks: Hardline - Warlord PRO - Marathon

Class 2 has STONER63
Perks: Lightweight - Warlord - Tactical mask

So when you follow this tutorial you can make it like:

Class 1 has AK47/GOLD CAMO
Perks: Hardline - Warlord PRO - Marathon

and OVERWRITE class 2 (A COPY OF 1!)

Class 2 has AK47/GOLD CAMO
Perks: Hardline - Warlord PRO - Marathon

Now: You cant change the gun and let it have camo, you have to rebuy.
You can for example do this:

Copy gold class then

Class 2 has AK47/GOLD CAMO
Perks: Hardline PRO - Warlord PRO - Marathon PRO

Class 1 has AK47/GOLD CAMO
Perks: Hardline - Warlord PRO - Marathon

This way you can maintain your weapon with gold.
The gun CANT be changed without rebuying.