I read somewhere on one of the forums, probably in the PDR7 forum, that you can select a transition and then make it a favorite.
After you have added a transition to Favorites, then select the Favorites group from the dropdown list of Transition types.
Click on the Library menu icon (with the green down arrow) and select Apply Random Transition Effect to All. With only one transition effect in the favorites group, then that will be the only transition that is used.
So that takes care of applying one transition to a group of photos. Then to add more photos with different transitions you can follow these steps.
1. Save your project.
2. Select File > New Workspace.
3. Set up a new favorite transition, add photos to the timeline, and apply the favorite transition as a random transition effect to all.
4. Use the Range selector to select all clips on the timeline and then click the Copy button.
I don't save the temporary workspace (File > Save Project), but you can before proceeding to step 5.
5. From the menu select File > Recent Files, and then open the previous project saved in step 1.
6. Move the Timeline Slider to the position where you want the clips to go and then click the Paste button on the left side just above the timeline ruler.
If you have more photos, the just keep repeating from step 1.
I guess the main point is that you can copy and paste from one project into another.
The other thing you could do if you already have the timeline filled with all the photos you want to use, is to select a group of photos with the Range selector and then Cut them. After that you start with step 1, and then after step 2 you click the Paste button.
Do not use the Cut (CTRL-X), Copy (CTRL-C), and Paste (CTRL-V) commands that are on menus. They sometimes don't give the same results as using the Range selector Cut, Copy, and Paste buttons.