If you want to edit the information for multiple songs, you can do this from the song library. Select whichever songs you wish to edit (with the Shift or Ctrl keys), then open the song information dialog:
Select Song Info... from the Song menu of the library
Hit Alt-Enter in the song library
Right-click on one of the songs and select Song Info... from the popup menu.
The normal Song Information dialog will appear, but will have some extra controls.
You cannot edit certain items for a group of songs - such as title, key, CCLI number, etc. These controls are disabled.
The main difference from the single-item Song Information dialog is the addition of checkboxes next to each item you may edit. Any properties that are already identical between the selected songs will be highlighted in yellow with the checkboxes set. Any items that vary from song to song will be blank and the checkboxes unset.
If you wish to edit any information on the group of songs, you must set the checkbox for that item before you click OK. Basically, if it's yellow, it will be overwritten.
In the example below, the Tempo, Topic, Words By, Music By, and Copyright Info properties of this group of songs will be changed. None of the other properties will be changed, even if they are different from song to song. None of the songs' contents will be affected.
Click on any item below for more details. More information about the various song properties can be found here.