Correctomundo.
Changing the GVWR for a truck can be done but is not inexpensive. I understand that it's a hassle to try to do a GVWR change through a dealer. Upfitters, by the nature of their business, have to change GVWR routinely usually raising it to accommodate new beds/boxes installed on a cab/chassis vehicle. Sometimes GVWR is lowered to reduce registration and/or insurance costs--more paperwork.
I've always heard that also but.........that isn't what a company certified vehicle alterer/modifier for LDT/MDT upfitter for utility bodies company told me. I asked him what it would take to uprate a '05 2500 Dodge/Cummins 9000 GVWR to a 3500 SRW 10100 GVWR. He said NHTSA rules won't allow raising the trucks GVWR but he can lower GVWR. My question to him was if I add all of the upgrades that Dodge uses on the 3500 SRW truck could he issue a higher GVWR.
This from NHTSA:
Frequently Asked Questions
on the Exemptions to the
Make Inoperative Prohibition
(snip)
.. the weight of all equipment that will go into or on the vehicle,
.. the size of the client and his or her mobility aid(s), family, and
.. whether additional objects/cargo will be added to the vehicle for recreational or other activities.
To determine whether a vehicle exceeds its GVWR, NHTSA's rules specify that only 150 pounds must be allowed for each designated seating position regardless of the weight of the intended users. However, consideration of the items described in the bullets above will help you deliver a vehicle that is not likely to be routinely overloaded by the user.
This information should then be used to calculate whether the modification would cause the vehicle to exceed the manufacturers Gross Vehicle Weight Rating (GVWR) or Gross Axle Weight Rating (GAWR) when in normal use. If it would, the vehicle should not be modified. Note: The "make inoperative" regulation requires modifiers to notify consumers of a vehicle's new load carrying capacity, if the load carrying capacity has been reduced by 220 pounds or more."
I ran into the same issue with a 18k tripple axle trailer just this summer. I upgraded the axles from 6k to 7k and asked the manufacture if he could resticker the trailers GVWR from 18k to 21k even tho the trailer uses the same frame according to the manufacture. He also said no but he can issue a lower GVWR sticker. He says once the trailers GVWR has been issued to the state for registration he cannot issue a higher GVWR tag.
Your state can give you the skinny on their altering rules.