1st. Select only the chassis only.
2nd. Copy & past the chassis.
3rd. Cut all the stuff that isn't a part of the chassis.
Here the trick of that pic.
4th. select the place where you want to see the color chosen on the body.
5th. Put a good amount of feather
6th. Go to Hue/Saturation & play with the colorization.
7th. Do select inverse, like that the color of the body will be equalized.
Carbon Fiber
Change rims
Change colour
I can, but I'm not very good, put bumpers from other cars on
Lower the car
Tint the windows
Turn lights on
Day/night transition
To cut a long tutorial short...
* select bumper that you want
* copy and paste into picture you want the bumper
* should automatically make a new layer. select bumper.
* move it over other bumper
* use the Transform > Rotate to get it on the right angle
* delete parts of new bumper that aren't needed.