No formula can refer to same cell where it is. So yes, in case you want to overwrite the value without storing original one somewhere, then VBA is only solution.

When you want really to do this, then consider a procedure which is run manually or is called by open event of workbook at start of every year. When you use e.g. workseet change event, then the code is run every time you edit anything in any cell on worksheet. This may slow your workbook down considerably!

Or user simply enters formula instead of date into cell. Something like