You can, though it may be tricky.
Just double-click a slide with the collage, then click Add Layer > Photo. You will need to animate the new photo manually, though. Alternatively, you can select a photo from the list of layers and click Duplicate. https://i.imgur.com/Qpn5izK.png
Then switch to Layer and replace the photo. Position this image on the slide to your taste.

If you need a detailed guide, contact our Support Team: https://smartshow-software.com/support.php