[Help needed] Add liveries to a vanilla car - Schafter

[Norberoo]

Hello everyone,
I want to make some liveries for "Schafter 3". As far as I am concerned about this vanilla car - it has not any liveries at all by default. I've read about it on some modding forums and I concluded that I need to kind of "enable" the car liveries availability by:

1. Editing the "vehicles. meta" file and adding "FLAG_HAS_LIVERY" in-between <flags> <flags> for "SCHAFTER 3"
2. Editing the "carvariations.meta" file, by swapping some values from "false" to "true" i believe.
3. Painting the car with some shader, if I am correct it is called "Vehicle_Paint3" or something similar.
   The 1st point is very clear for me, I've already done it. The problem occurs when it comes to the 2d one. I do not know how to properly change the values, and which values should I change, etc. 3rd point seems to be problematic as well. The thing is that I am pretty much a rookie in ZModeler3 and I have no idea how to do it. I am looking for somebody that would like to teach me basics, show me some "tips and tricks" for ZM3, etc.
   (https://forums.gta5-mods.com/topic/807/tutorial-accepted-multiple-liveries-methode-for-any-car/2?page=1 <- a tutorial that I've found)
   I would appreciate any kind of help!
   Thanks in advance!