The Problem: you would like to rename one of your many Google Reader tags/folders, but Google Reader does not directly allow this.
The Solution!
- Open Google Reader
- Open the Settings page of Google Reader, then go to the Subscriptions tab.
- Enter the name of the existing tag you wish to change in the input field called “Filter by name, tag, or URL” (top right)
- Click Select: All -X- subscriptions (top left)
- On one of the subscriptions, use the menu called “Change folders...” to create the new tag (renamed version of existing). This is done by clicking on New Folder...
- In the “More actions…” menu at the top of the page, choose the new tag under “Add tag…”. This will add the new tag to all selected subscriptions.
- In the “More actions…” menu, look under “Remove tag…” and select the old tag to remove it from all selected subscriptions.
- Done!
Thanks again to Haochi.