In MS Excel, How can I use a date to trigger a cell to display a number?

I am working on a project in Excel with a number that will be outdated once past a certain, ascertained calender date. Once this ascertained date is reached, a new number must replace it. Currently, (before I started working here) we have been doing this manually year after year. Is it possible to create a formula that would automatically trigger the change of numbers based on the date?