I want to know if there's any way of putting more than what's in the archive into the file? I don't want to get rid of the police cars I got, and I got more than what this game has. Is there any way of doing that?

If you mean add a car to a new slot and not over write anything else there is.

Though it is beyond my skills.

You can add a "newvehicle.img" to pc / cdimages / models as well as the existing "vehilcles.img" but you then also need to make new entriess for that in several other places. carcols - cargrp - default data - as well as add a "newhandling and newide" files.

Like I said it's all beyond me just repeating how I have seen it done.

I had a mod that used this and meant I was the only person who could drive it. The AI were unable too as the model had to be spawned with trainer.

When I got time I will try and find the download for that model so you can see how it was done and what was needed.

PS: not saying this is the only way, it's just the only way Iv'e seen.