For the energy dashboard I have input numbers with the cost per kWh / m^3 for my energy and water.
These rates currently change every few months. I know when they change into what value. But currently the only way to be sure the calculations are correct I know of is to change the input_number values exactly at the time the tariffs change, manually.
Is there a way to schedule such changes? That way I have to setup it beforehand but the execution will be right on time.
Sure, use a time triggered automation and use the input_number set value service.