There are lots of different places in Carmageddon where you can hack into the files and change a few things to increase the fun or make the game easier and just a reminder, any damage any of these hacks do to your computer or anything are not my fault. You may want to make a backup copy of the files before changing anything. For any of these hacks to work, you have to go to the game screen that gives you race info and whatnot and type in "IWANTTOFIDDLE" Carmageddon is very Crash Prone after you start hacking it, so be careful.
Permanent Free Repairs
First open the Carmageddon directory, then open the data folder and open the General.txt file. Go down 15 lines and you will see the numbers 10, 20, and 30, change these numbers to 0 and no matter what level you play at, all repairs will be free.
Permanent Free Recoveries
Open the Carmageddon directory, open data, then General.txt. Go down 16 lines and you will see 1000, 2000, and 4000, change these to 0 and no matter what level you play at, all recoveries will be free.
A mean hack
Open the General.txt file and scroll down until you see cars to use as defaults, then go down 4 lines and you will see the number 1.0. This value is for the opponent nastiness. Change the value to something like 100 and all of your opponents will come after you like old women after an old men on Viagra.
Many other hacks in General.txt
If you go down through the rest of the General.txt file, you will find many different values that you can change. Just read the discription of what the values do, just to the right of the values. Don't make your values too large though, you may crash the game.
Open the Carmageddon\Data directory, then open Powerup.txt. Each of the sections is a different power up, in the powerups you can change how long they work for, 1-whatever is the number of seconds, -1 is just for a second, like instant repair, etc., and 0 lasts forever. Don't change the powerup sections that are really long though, they are the random powerups.
Get all car power-ups for cheep and at any level
Open the Carmageddon\Data directory, then open Partshop.txt. Each of the columns with numbers in them are the ones you are going to change. The first column is the rank you have to be to buy the powerup(don't change the 6's though). Change them all to 99 and you can buy all of them at the beginning of the game. The third, forth and fifth columns are how much the powerup will cost. Change them all to 1 and the powerups will be CHEEP.
Open the Carmageddon\Data directory, then open Text.txt. You can change all of the text in the game. Change them to your liking, I suggest much profanity.
Open the Carmageddon\Data\Cars directory, then open the car of your choice. I suggest that it be either the eagle or a car that you already have in a saved game, otherwise after you hack the car, you may not be able to win a race with against it. The file name of the default eagle is blkeagle.txt. Go down through the lines and change the damage from certain impacts to the available areas of the car to 0. Then scroll almost all the way to the bottom of the file and change your center of mass values to 0 so you get better handling. Also change mass in tonnes to a high value like 100 or so. You can also change your top speed to a high value, but I doubt that you can keep control up near 1000 mph. You may also change the acceleration to a slightly higher value to simulate a bigger badder engine. You can mess with a few other values, but don't mess around too much, the game could crash.