In Canada its simple.
You have 3 numbers on the door sticker
Front axle max weight
Rear axle max weight
And gvwr (total max weight of the truck)
By law here, you are not allowed to exceed any of those 3 numbers. Even if your right on the max gvwr of say 9900lbs for a srw f350, but all of that 9900lbs is on the rear axle (hypothetically) you would still fail being weighed at the scale because the tag says of that 9900lbs only 7'500 can be on the back axle.
Plus adding air bags, sway bars, 19.5 tires, does not change any of those numbers in the eyes of the dot. Contrary to popular belief.