Adding, Removing And Renaming A Label Across Multiple Posts

You can add, remove or rename labels without entering into each individual post. You don’t have to do it post by post, it can be done across multiple posts, in one go.

Update Sep. 2011: Add instructions for new user interface.

To do this, go to Dashboard > Edit Posts tab. Notice all the labels used in your blog are listed on the left side of the screen, under Labels. On the right is the list of your blog posts. Each post has a checkbox next to it.

Adding a label

To add a label:

1. Select the posts you want to apply the label to by ticking the checkboxes.
2. Click on Label Actions… dropdown menu, then select New Label... .
3. Enter the label in the Enter New Label text box and hit OK.

Removing a label

To remove a label:

1. Click on the label (in label list) you want to remove. All posts containing that label will be listed on the right.
2. Select all posts by clicking Select All link on the right of Label Actions…dropdown menu.
3. Click on Label Actions… dropdown menu, then under Remove Label, select the label to be removed.  

Renaming a label

Renaming a label is a combination of adding a new label and removing the original one:

1. Click on the label (in the label list) you wish to rename. All posts containing that label will be listed on the right.
2. Select all posts.
3. Click on Label Actions… dropdown menu, add in the new label .
4. Lastly, remove the original label.
5. Reminder: Add in a new label first, then remove the original one, as explained above. Don’t do the other way around.

Label actions via new Blogger user interface

The process is basically the same with just a few things moved around.

• On the Dashboard, click the gray Post List icon (that looks like a sheet of paper) next to the blog you want to edit the labels for. It will list out all posts for that blog. 
  
• To filter the list according to specific label, select a label by clicking the All Labels dropdown menu at the top right corner of the page. 
  
• Adding and removing a label can be performed by clicking the Label icon on the left of the Publish button. 

source  :  http://www.bloggersentral.com/2009/10/adding-removing-and-renaming-label.html