They've said:
We will be more than happy to look into the issues that you are having. I would first suggest swapping the exhaust back to standard and try that. We cannot deem anything modified as warranty. Also, if we find that there has been a remap previous to you purchasing the vehicle, this has warranty implications, too. We have spoken to Porsche regarding your GT3 and this is what has been advised.
The over-rev is on the vehicle analysis log for the history of the vehicle. There may be still coverage in terms of warranty, but extra checks have to be carried out before Porsche will agree to warranty.
Quite why they are suggesting there was a remap before I bought it I've no idea as it was me that put the exhaust on recently and they've had clear details on this.