I want to buy the 2008 Ford Mustang through Carmax but...?
You can, but its really quite expensive. You can buy the kit and install it yourself, or you can get ford to install it. I have the mycolor option in my mustang and its pretty nice, I do not have the colored cupholders/floor lights though. But yes, you can add it after you buy, but I think you should buy the mustang and save the extra $$ for modifications! (exhaust, cai, tuner, etc) check out mustangforums.com or allfordmustangs.com for ideas!