How do you add a tag to an existing Facebook status?

[ebeth9161971]

I posted a status a few hours ago on FB and am now realizing that I forgot to tag a few people in the status. How do I go back and add their names in the original post?

[Matt]

Sometimes, you can edit them by clicking a down arrow to the right top corner of the status but usually you can't. Best is to just tag the persons name in the comment section by write @John Williams for example.