How to create slightly improved vanilla weapons?

[RAGE PVE]

Is there a way to replicate these vanilla weapons and create customs out of them but add on like 10% of DMG etc?  T6 are what stats I grabbed by spawning in-game (using bundle box!) and the T7 are like 10% increase but 5% on durability but problem is the spawns can vary quite alot!

We're trying to create some consistency in the weapons but wondering how to dictate the stats we would like and how to prevent them making rng, seems we can only know for sure when we enter the game each time so if its wrong its a bit of a pain.

If anyone has done this before or knows the best way to tackle then I'm all ears, I'll also extend this to a bit of a request if anyone fancies taking on make a bunch of these weapons at all? 

gunMGT3M60
gunMGT2TacticalAR
gunHandgunT3SMG5
gunMGT1AK47
gunHandgunT3DesertVulture
gunShotgunT3AutoShotgun
gunRifleT3SniperRifle
gunHandgunT2Magnum44
gunHandgunT1Pistol
gunRifleT2LeverActionRifle