Vehicle Engineers reports, 4WD Modification rules, whats allowed, what not...

[the evil twin]

snip....
[/I]Where the original GVM of the vehicle is no longer applicable due to the modifications
performed, a new GVM must be determined.[/I]
So I assume this is what they will be doing with mine as its had the motor changed which has resulted in an increase in weight. Something I will ask them for sure.

Nope... your GVM will still be the same.
Your Tare and Kerb Weight may increase and your Payload decrease accordingly but your 'original' GVM will only change if the Modification affects the GVM so the 'original' is 'no longer applicable' such as an engineered GVM upgrade

Think of it like a 20 litre bucket and for the example assume the bucket alone weighs SFA (tare).
The manuf says this bucket will only carry 20 litres of water equal to 20 Kg as any more and the handle will break (original GVM is 20 Kilos)
Sooo...

Ex factory it carries up to 20 litres (payload) and weighs up to 20 kilos (original GVM) = handle is good

Put in a 5 kilo brick (say an engine modification) this increases tare 5 Kg, bucket can now only carry 15 litres of water (payload) but brick plus water still weighs 20 kilos (mod doesn't affect GVM) and pick up bucket = handle is good (even tho there is still capacity in the bucket for more water)

Now, top the bucket up with some more water so bucket weighs, say, 24 Kg (GVM) and attempt to pick it up (get pulled over by scaleys) = handle will break (Scaleys give you a bluey for being 4 kilos over GVM)

Buy a stronger handle (a mod that does affect GVM ) rated to break at 25KG with a certificate for bucket. Now with brick and water it weighs 24 KG (1 Kg under the new 25 Kg GVM) and pick it up = Handle doesn't break (all is good and scaleys give you a hug)

P.S. where do I send my Consultancy Invoice?