Again, for your upgrade, the correct answer is you do not have to. It is an engineering function and if you have no modified W&B figures issued then don't accept the aircraft.
Of course, if we are talking 'life and death and drama' stuff then you would have to modify it yourself, but a bit fanciful, don't you think? Mind you, if I were in that much of a hurry I'd whack on a bit more trim and go without a loadsheet!