Well heres what you do...
1. Use CabExtractR2
2.Transfer Cars.ca2 from the CABS folder onto your computer
3. drag the Cars.ca2 file into the CabExtract.exe and then it will start to extract.*note that the extraction is most likely going to be about 1-10 minutes
4.after the file has been extracted, in the folder the cars.ca2 file was there will be the extracted files such as Engines and cars.
5.now ALL of these extracted files are XML types so its pretty straight forward on editing it. ***There are some files that wont show up right and will give you symbols and signs like this ""***
Well I hope that this litl tutorial cleared up most of the questions on how to edit cars.
Also please do not tell me if something does not work because this is only somehting that is just a start and isnt something that has been going around for a while