Early releases from the developers of the "Grand Theft Auto" video game series suggested that it would not be possible to customize cars in "GTA IV." The designers might have caved into pressure, or they might have been releasing misinformation deliberately. Either way, there are customization options available, although they are not as extensive as they were in earlier releases. A car’s performance can be changed with the application of bullets to certain parts of the car, but these performance changes do not generally give a "GTA" player an advantage.
How to Customize
Turn off "Police Mode" and turn on "Free Mode." This will give you fewer potential distractions when finding a place to take one of your stolen cars for a new paint job.
Take the car to one of many hard-to-find paint shops, which are named Pay or Spray.
Select a new paint job for the car. Unfortunately, players cannot use their own custom paint job. PC gamers may be able to figure out a hack that allows more options.
Pay the man. Of course, no body shop is going to work for your car for free in real life. You don’t expect a virtual body shop worker to work for free either, do you? (Many of them have virtual families to support.)
Take your new car out onto the street. This allows you to show the world or at least your friends your gaming prowess and your ability to find one of the few Pay and Spray paint shops in the game.