Being over charged vehicle tax 405 p/a

JQ.

If they allowed you to do what you propose, it would create a nightmare. I have an aftermarket ECU in my car that is fully tunable, I've no doubt I could get a very conservative tune, get the car emissions tested and then re-tune it for power, saving me a fair bit of money and defrauding the tax man. It would create a whole business for people re-tuning cars for short periods of time just to get a low emissions certificate then having the original tune re-installed once the emissions test is complete.

I assume you did get the car cheap in the first place, in which case surely problems like this were factored into the price you paid?