Changing length of already imported stills

I'm making a slide show video. I imported a bunch of images at the default lentgh (5 secs). I did one edit, during which I decided the clips should last a  biit longer. I found out how to do that en masse with clips in the sequence and all was good.

Now I'm making a second, longer version of this same video and have imported additional images to expand it; again, with clips imported at the same default length. Then, since I already knew I wanted the clips 7 secs intead of the 5 sec default, I thought going to Prefs and setting a new default to 7 secs would be applied when the still is placed on the sequence not knowing that, in fact, the default was already applied upon import and that's that. Changing the time in Prefs will only apply to clips not yet imported (you prolly already knew that)

So my question: is there any way to change to the duration of ALL already imported clips?