The GVWR on your vehicle is "as equipped" from the factory. You can certainly upgrade your vehicle in any way you choose, but for the weight to be legal you must have your work inspected and have a new GVWR assigned to the vehicle which will show on your registration.
Actually that is not true by any means.
The GVW isn't changed by anyone except a manufacturer or an upfitter following the manufacturer's guidelines - and the latter is only within the rated GVW of the manufacturer.
I have been over this subject with several groups who regulate and manufacturer the vehicles and they all say the same thing -
the sticker rules.
SO the only one that can issue the OEM sticker is the OEM and the upfitter's issue a supplementary sticker with any modifications for the vehicle, like altering the wb.
The inspecting officer doesn't care about the registration of the vehicle, they go by the sticker and only the sticker. If the sticker says 9600 lbs, it is 9600 lbs, nothing more. Registrations are tax receipts for licensing, not any proof of that safety standards are followed.
NOW the other side of the issue is this, the equipment that you retrofit onto the vehicle may not be up to the standards of the manufacturer, like air bags or more springs. This means that unless the manufacturer of the equipment you put on the vehicle meet the requirements, you are doing so at your own risk.
If you expect anyone to inspect those modifications, it has to be the manufacturer to ensure that the parts used are up to their standards and are tested to meet the requirements they feel are necessary to increase the weight.
Will they do this?
NOPE, not a chance in hell they will do that for anyone except "special customers".