how to add liveries to a car that does not have them?
first, this shouldn't be in requests.
second, read the reply i gave you on your comment on my livery
As Reacon so friendly pointed out it has to be UV mapped in zmod3 which is the software tool used to convert vehicles from other PC games into GTA V file format yft and ytd.
UV mapping means the bodyshell of the vehicle is layed out to a template so you can apply a Paintjob to it
Vehicles that have this are tagged on the 5mods page by having [Template] in the title