They could change it, but it could present problems. Namely it voids any penalties for cancelations and a few other issues. Like if you have an NRD at sideshow and they change something that's integral to the figure, or specially spelled out in th presser (press release) then sideshow can not enforce the NRD, and if you cite it as a reason to cancel they have to refund it and it can not be held against you in any way(like when they tell you when you cancel an order and they transfer the NRD that it's only a one time thing. Well with this type of situation they can't hold it against you in that way). Of course 99% of store owners and CS reps(both at sideshow and other places) don't actually this so there's that you have to deal with. Lol And the same holds true for any company/store that orders multiples and cancel at the distribution hub claiming a major change cost them sales. There are penalties and clauses written in to each authorized dealer and distributors contract that get voided by that stuff.
So there's nothing that stops them from changing it, and most people don't know what the factors are that are impacted by it anyway...but it's just a risk companies don't like to take.