Hi Alex, hope you're well mate. I've got the MTM Cantronic box which can be reflashed but to be honest I think I'll be going for an O2 sensor spacer - either CTS, 42DD or even an eBay special?I'd look at what has changed to cause the CEL... I think your sport cat is throwing lambda readings off which is causing the light. You need to scan the ECU with vcds to know for sure. If it is the sport cat that's the problem, you may need the ECU map adjusted.
Get it scanned to find out the exact reason for your CEL.
Sent from a mobile device, please forgive typos