When is it too late to make changes?

My car is a March production. I wanted to make a small change (add the storage package, a "feature" that is standard in most of the world but deleted in the Canadian model).



I called today and my sales person said the car is "in production" and that no changes can be made.



i just wanted to make sure he wasn't BSing me!



Is this nornal or should I be able to make changes?