I had a guy around from EON last week to read the generation meter so it is happening.
They don't care how much you actually export; I've had solar diversion for almost as many years as my PV system, a battery storage system for over two years and now a BEV car and charger capable of diverting any excess to that too. Basically if I'm exporting then I'm looking at ways to stop that! And by doing that, you aren't doing anything illegal.
The only thing you can't do is change the size of the array or type of panels. If your inverter breaks (and it likely will - mine did) then you can also replace that with anything you like without notifying them - the only catch is if you have an array > 3.6kWp and are restricted by your DNO to that limit - in which case you need to ensure you are staying below that.
If your generation meter breaks (and they can do), then the FiT provider just normally needs the old meter reading (if you can provide it), the new meter serial # and new / starting reading.