For that you can use an asset…and when you need a different date pass a value in asset else pass asset as NA and when it is NA use the current date else use the input date from asset…
This way you need not change anything in the code as well. You only need a if condition to check if asset is NA or not
For options go to excel → options → formula → you will find a calculation formula tab …can change the values to automatic there or as required
Cheers