WOW, tough crowd. You are correct again, forgot the R, thanks for pointing that out.
Again the GVWR can only be changed by a front line manufacture. This has to be done prior to taking delivery of the vehicle. I am pretty sure of this although I have not been able to find it yet. It may be different for other states, but pretty sure it is a federal reg.
Yes it can be changed, when for example a truck is purchased and then sent to another manufacturer for modifications, such as a well drilling unit. This has to be done prior to taking delivery of the unit. Modifications can still be done after taking delivery, however you will not be able to change the GVWR.