I am trying to prefill a field with the value from a previous field in the same form. (I want the last name of the wife to be prefilled with the last name of the husband that had already been entered.) I have been able to do it by making the husband's last name a variable and then using that variable as a calculated value to prefill the last name of the wife. It works, but it doesn't give the wife the ability to change the last name if hers is different. There was a previous post referencing the ability to allow the user to change the value by deselecting the "Lock" option next to the calculated value. There is no option to Lock or Unlock next to the calculated value.
Is there any other way to prefill within the same form?
No, we've removed the ability to edit the result of a calculation on the form. It would not be possible to do what you describe without custom code. If you still need support with it, please open a support request with us.