I *think* that regardless of what is ordered (upgrade or not) the chassis is the same and the potential for that chassis is the same therefore the plate should be.
Happy to be corrected on that though.
I suspect the chassis and so its maximum "potential" remain the same. That must be the case where "upgrading" is offered post build without any physical changes.
However, if the legal type approval plates are identical, ie contain the same maximum weight, how then can the industry play the down grading trick?
That is, plicating, driving licensing limitations, car towing limits, possible Insurance restrictions and the UK's 85% ratio obsession? Much of that being based on a plated MTPLM, as Lutz points out you can't have differing MTPLMs, it is an absolute value. You can credit a particular van with a lower MTPLM than the potential maximum, but not share that Type approval's MTPLM.