Need upgrade template for workshop mods.

Hello guys.
I go straight to the point: I want to modify some workshop car mods, making an upgrade and then share it through the workshop.
For example, introducing a six manual speed version of the RUF Yellowbird and also the option for the 4WD with the rear split torque used by Porsche in the same model of those years.
Or upgrading the Alfa 155 DTM with new mass and inertia, 4WD, 11200rpm engine, new set of gears and tires compounds.

Do we have some step-by-step guide/template for it?
I was searching in the forum, but the informations aren't complete.

I make an example. Got a car in which I modified the hdv file, the chassis.ini, the engine.ini, the gears.ini, the tires.tbc and also replaced the original compound.tgm files with new ones.
This is the file with the HDV modificated lines:

UpgradeType="Drive Type"
{
UpgradeLevel="RWD"
{
Description="Rear Wheel Drive"
}
UpgradeLevel="4WD"
{
Description="Four Wheel Drive"

HDV=[GENERAL]
HDV=GarageDisplayFlags=58
HDV=Mass=1175
HDV=Inertia=(1370.5363,1540.4995,211.9874)
HDV=
HDV=[PITMENU]
HDV=FrontWing=1
HDV=Radiator=1
HDV=TrackBar=1
HDV=CompoundRestrictions=0
HDV=
HDV=[BODYAERO]
HDV=WaterRadiatorRange=(1,1,5)
HDV=WaterRadiatorSetting=1
HDV=OilRadiatorRange=(1,1,5)
HDV=OilRadiatorSetting=1
HDV=
HDV=[CONTROLS]
HDV=HandbrakePressRange=(0.5, 0.1, 6)
HDV=HandbrakePressSetting=5
HDV=
HDV=[ENGINE]
HDV=Normal=new 155 engine.ini
HDV=
HDV=[DRIVELINE]
HDV=WheelDrive=FOUR
HDV=FinalDriveRange=(0,0,3)
HDV=FinalDriveSpecial=(0,,,"1000,6800,1,1")
HDV=FinalDriveSpecial=(1,,,"1000,5500,1,1")
... etcetera
}
}

How do I point the other modified files and the new tgm files in the upgrades.ini text file?
Also, I know that I have to package both the original files and the new ones in a mas file and then package it. But do these mas have to be two, one for the originals and one for the new, or can I put everything in a single mas? And in this case, how can I compress everything in a single mas without overwriting the originals hdv, ini and tbc files?

It's a lot of questions, so if someone knows of a guide somewhere would be great.
I read the upgrade file from some cars, but it's mostly graphical stuff on GEN files, while many others are already contained in the mas file of the car.
Like this one form the Audi IMSA GTO of the workshop:

UpgradeType="BOP"
{
UpgradeLevel="740HP"
{
Description="IMSA 1989"
}
UpgradeLevel="460HP"
{
Description="BOP to compete whit Toyota Celica GTO"

HDV=[GENERAL]
HDV=TireBrand=G_2.tbc
HDV=
HDV=[DRIVELINE]
HDV=FinalDriveSetting=4
HDV=Gear1Setting=1
HDV=Gear2Setting=15
HDV=Gear3Setting=36
HDV=Gear4Setting=57
HDV=Gear5Setting=70
HDV=Gear6Setting=77
HDV=
HDV=[ENGINE]
HDV=EngineBoostRange=(0, 1, 5)
HDV=EngineBoostSetting=0
HDV=BoostTurboPressure=(180000,5500)
HDV=GeneralTorqueMult=0.520
HDV=GeneralPowerMult=0.610
}
}