So, i'm not sure if i got you right. What exactly do you need?
1. You have preplaced doodads and you want to change the variation? Should they all be the same afterwards or just "Reroll" -> you have to manually click them, if you want to change them to the same variation, you can group select them
2. You want to choose which variation you get when you place them -> select the doodad and disable the "place random variation" check on the left side above the preview window
3. something else?