The yellow payload stickers were added to make the manufacturers liable for their products and to make the information readily available by the consumer after the Firestone/Explorer rollover issues in the late 90's when Ford was blaming Firestone and Firestone was blaming Ford. It's only a certification sticker imposed by the NHTSA on the manufacturers to inform the consumer of the vehicles weight recommendations off the show room floor.
There are many things that can alter the number on the door like a lower tire pressure than what is recommended on the sticker or replacing the tires with a lower load rated tire. You can also remove items off your vehicles and/or replace them with lighter parts which would also alter that number. This is why the number on the door is not enforced by law for non-commercial vehicles due the many unknown variables effecting the number, and instead it is the GVWR that your vehicle is registered for that is enforced.
If you want to be within your GVWR, then the best thing to do is fill the tank and weigh the truck with you in it. Subtract that weight from your GVWR to get your payload. Then adjust for any weight you add or subtract from that point on.