Thanks to some hard and awesome work by This, that and the other (a.k.a TTO), the long-requested feature of allowing users to add and remove change tags (see T20670 https://phabricator.wikimedia.org/T20670) has been merged and should be rolled out with 1.26wmf3.[1]

Tags defined by MediaWiki or extensions, such as "HHVM", "visualeditor", or "mobile edit", cannot be added or removed by this feature. Only tags specifically activated for the purpose may be added, and only those tags or tags that are unknown to MediaWiki beyond being on some existing revisions may be removed.

Management of such tags is already available to users with the 'managechangetags' right (admins by default) via Special:Tags.

Tagging and untagging of individual revisions and log entries will come with 1.26wmf3. Tags may be applied by users with the 'applychangetags' right when making an edit,[2] and existing revisions and log entries may be tagged and untagged by users with the 'changetags' right via an interface much like that for revision deletion. Both of these rights are granted to all logged-in users by default.

If the default assignment of these rights is a concern for the community of any WMF-hosted wiki, please follow the procedure at https://meta.wikimedia.org/wiki/Requesting_wiki_configuration_changes to request the necessary configuration change.

For API users, the relevant modules include action=managetags, action=tag, and action=query&list=tags.[3]

[1]: See https://www.mediawiki.org/wiki/MediaWiki_1.26/Roadmap for the schedule [2]: By default there is no UI provided on the edit screen, but gadgets may add a 'wpChangeTags' field with a comma-separated list of tags. API users may use the new 'tags' parameter to action=edit. [3]: See http://en.wikipedia.beta.wmflabs.org/w/api.php?action=help&modules=manag... for help, and post questions to mediawiki-api https://lists.wikimedia.org/mailman/listinfo/mediawiki-api.