Authors of Facebook Places check-ins can now tag additional friends in an existing Places check-in through the Facebook web interface. Check-in authors can also remove tags of other individuals from the check-in without deleting the check-in itself. The change will help users cumulate friends as they arrive at a location into a single check-in story with high prominence in the news feed, or remove friends who didn’t want to be tagged.

Previously, if you had already created a check-in and more friends arrived at your location, they would have to create a second, separate check-in. These stories were sometimes compiled into an aggregated check-in feed story, but if all your friends are intermingling at the location, it’s more accurate to show the check-ins as one story. Tags can be added as long after the initial check-in as a user wants, so if the next day you find out more friends were at the same baseball game as you, you can add them to the story. Adding tags does not appear to extend the initial three hour “Here Now” duration of the check-in.

The author of a check-in can also remove other friends they tagged from a check-in if they later decided they didn’t want to be associated with someone, or if that friend didn’t want to be tagged. Any user can still remove themselves from a check-in. The added capability is applied retroactively, so you can edit check-ins made before the change was made.

To add or remove friends, view the check-in on your wall or the Places page of the location through Facebook’s web interface and click the new “Tag Friends” button next to “Like” and “Comment”. This brings up a multi-friend selector where users can add or remove friends through browsing or search. Once the edit to the check-in is saved, added friends will receive a notification, and removed friends will have the check-in story removed from their walls.

You can’t add or remove friends from a check-in through the Facebook for iPhone or m.facebook.com mobile interfaces — the only native interfaces from which you can create check-ins. This means users must either access the full site via a mobile browser, use a computer if one is handy, or wait until you get home to edit their check-in.

A final note: this change is one of the first made to the Places interface since the launch of the product. Facebook has been focused on releasing the feature in more countries, but now it seems ready to implement feedback and give users more control over how they share their location.