Drive off track
On Sears Point Raceway, go for seven turns (or eight if you count the little tiny dip in the track as the fourth turn). Stop after the area of sand at the end of the seventh turn. You will be able to get into the space between the tire barrier and the fence there. Drive along that place for a short while until the fence ends. You should now be able to drive around on the dirt outside of the racetrack with no boundaries (except the edge of the ground).
No roof flaps
Before You start with this keep in mind that this procedure involves editing a game file; create a backup copy of the file before proceeding. Now, in the game folder, open the folder with your player name. Use a text editor to edit the file "player.ini". The first number you see should be "1". Change it to "0". When you play the game and go backwards at a fast enough speed, you will fly into the air and possibly do some flips.
Cops and robbers
Go to "Opponent Manager", select a car from 101 to 140 (not cars 1 to 99 or they will be deleted and you will have to reinstall), and go to "Paint Shop". Do not forget this car's number. Make this car into a cop car as desired, then export that paint job so you do not have to repeat that step. Then, put the cars original number on its back side somewhere to identify it, for events such as yellow flags and pacing times. Do this to all of the 101 through 140 cars, except the one that will be your car to drive. When done with the cops, paint your car as desired. Then, choose that car as the one that you will drive. Start a new race. At the pacing line, you should notice that all the cars are cops and you are the only one that is different. Get ahead of the pack and run, or get some good pile ups. Indianapolis is a good choice, the straight by the finish/starting line has a narrow road for some very good pile ups. Daytona is also a good choice, as it is an easy track to drive on.