Many times the 'Organize' tool does the job quick and easily.

For example:

1) Choose one album via 'Albums' tab, and click the album title.
2) Then use the drop down menu 'Edit these items' on top right.
3) Choose for example 'Keywords', and you can then define a new keyword to all images in that album at once.

Also try to use the 'Advanced search' feature above the bottom film strip. You can for example search and choose all images taken on the same month of a year, and change some setting for all of them.

More tips updated onto this photo article maybe later. If so, then this photo made to pop up as a new post.