The short answer is no. It is a crime to alter electricity meters. You are also putting yourself at risk by working on the main switch’s live side. You will not be pleased with the result (injury burns, amputations, death).
Long answer: The tariff meter is composed of two input and two outgoing wires. These are active and neutral, in or out. There are two circuits within the meter: a current sense circuit, and a voltage sensing circuit. You could also reverse the current sense to get the meter running backwards in the early days of electromechanical meters. To do this, you would have to open the meter and break the lead seal. Many people lost their lives due to the loss of their financial gains from the swap.
This swap is not possible with electronic meters. They are programmed to reject counting backwards. The meter will keep track of the power that is delivered to your home and also record the power sent to the grid. This is due to the recent introductions of solar cells and other forms domestic generation, e.g. Wind turbines. The “power in”, while charged at a specific rate, is charged at another rate. Both amounts are separately recorded and charged separately. One is a cost and one is a reimbursement. There is no way to reverse the meters as it was in the past.
Hacking firmware will require a lot of work and likely a long sentence in prison to regret not having done better with your time. The average meter is impossible to hack, I’d venture to guess. It is almost certain that the firmware will be embedded on the chip. Once the lock bits have been set, the chip becomes unreadable. It will be possible to wipe it (i.e. You can set the memory to zero, but you’ll have to create the entire tariff meter code completely from scratch. There is no guideline to help you with what it should do or how it communicates.