How do I set my new price/kWh but also keep old data

When I started using the Energy Dashboard, I entered my electricity price at the time to see the costs. But if I now have to pay a different electricity price from a certain date on and enter the new price, will all historical values regarding costs change? How can I calculate the costs using a new electricity price from a certain date, while the old consumption is still multiplied by the old price/kWh?