HI, jnorberry,
You can bulk change the duration of still clips, but not video clips.
To bulk change a range of still clips, select them as a group by selecting the first still image in the series and then hold down the Shift key and select the last clip. Then click on the information button (the little circle with an "i" in it) in the tool bar in the upper right of your screen. A duration box will appear to the right. Type in the duration that you want, e.g, 4.0 seconds. Then hit the return button on your keyboard. That will change all of the still images to the duration that you typed in.
Another way would be to click on iMovie/Preferences and change the Photo Duration to the duration that you want. Then create a new project and paste in your 137 clips. They will all bear the default duration that you set in preferences.
The only way to change the duration (length) of video clips, as opposed to stills, is to trim each one manually.
-- Rich