Of course. If you have the "trigger" field as Text1 and the display field as Text2 + the formula that you wanted to display in the instance of a blank trigger field was today's date you would use:
IIf([Text1]<>"",[Text1],Date())

This checks to see if Text1 is blank and if it is displays today's date but if it is not blank it displays what ever is in Text1.

To adapt to your situation simply replace the field names as required and change date() to your chosen calculation