Is it possible to autofill a period (.) at the end of text of a large column of existing text fields?

I have a column of about 4000 descriptive text fields that need to have a period dropped in at the end of each description. To ensure not losing the actual existing text, do I have to individual pop into each field and manual add a period (.) or is there a way to autofill without risking the data?

Thanks in advance for any insight!