I was reading something on the CAA site that says if you modify a drone that carries the new C mark then you will no longer be allowed to fly it based on the C permissions.

Once modified it will have to abide by the regs for the weight only.

In the case of the Mini 2 (or maybe Mini 3 before DJI start to classify them) then this is a good thing surely?

The unclassified Mini 2 gives you more freedom where you can fly than a C0 classified one.

So if you buy one that is eventually classified as a C0, all you need to do is modify it and then it will revert to the regs based on any drone with a camera below 250g.

I have attached the wording from the site. Am I wrong about this?

The problem is probably that once C-labelled drones start arriving they consider Maximum Take Off Mass rather than weight (as C-labelled drones will need published MTOM). For a Mini 2 (for example) the MTOM (if it were published) would be >250g. So DJI will need to make an even lighter drone to compensate.

Hello there marcel_911. Thank you for reaching out and for sharing these information here at DJI Forum. Have a safe and a happy flying always.

This is a very good point.