Do shop around, especially for advice. There are many "experts" out there who (probably though ignorance) will make statements which are simply not true.
I wanted to expand my existing 4kWpp PV to 10kWpp while staying G83 compliant and preserving my original FIT.
I was told it was not possible by one. I was told it was possible by another but only in zero export mode by another. Another said it could be done and then failed to deliver a solution. Finally I found Solar Southwest who delivered exactly what I requested and went on to fit a PW II. I could not have been more pleased.