For tires I know for sure you can buy and equip a race soft and buy every single tire option and then before each race be able to choose which tire you actually use.
I also saw that I had two different transimissions to choose from under tuning. The 15k credit tranny and the 20k tranny I upgraded to. I am not sure if you can swap between them like tires, but it looks like you can.
If that is possible, then any kinda upgrade like turbo, intake, exhaust......stuff you don't improve in a chain of upgrades like engine and weight....you can probably purchase the lower level upgrade and swap down to it. Removing it all together, I doubt it. But if you're just trying to loose some HP for better control....
