While it is true that you cannot buy parts in Prologue, once you defeat the three series( C, B, A) you can open up a quick tune option that allows you to make certain adjustments such as turbo boast, tire type, ride height and gear ratios. but you are correct in that buying parts and customizing the cars is a major part of the experiance. In the full game all of that will be available as well as online micro-transactions that will allow for the purchase of additional hardware to download and add to your ride.

I hope things are going well on your job!

TJ