How to convert the output of a formula in a cell to text in the same cell by changing a value in another cell

In cell B2, I enter values ranging from numbers and text. In cell C2, a date is entered based on the input in cell B2 by means of a formula. Initially, cell b2 will always contain a number first. The moment I enter an A in cell b2, I would like the formula in cell c2 that currently shows a date to be converted into text so that the date is no longer calculated based on the formula but that the date ‘freezes’ into a fixed date.

Addendum: The worksheet contains data to plan my actions. In the column Date (= column C) there is a formula that shows a date calculated on the basis of a number in the column Daily number (= column B). What I would like to achieve is that when the action is completed (then the letter A will appear in the column Day number) the date will appear as the date and not as a formula. Another option maybe is to add a column Date rounded to the table and automatically put the fixed date here when I put an A in the column Day number.

If you really wish to exchange the firmula for its result, you will need a macro. The format (text or number) will not matter.
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But maybe protecting cell can also help: