A long time ago, when I was using Photoshop Elelments I found a plug-in that made it possible to work with stacks as a unit.
If I labeled the top image in the stack that lable was applied to all the images in the stack; then when I sorted the images, the stack remained in tact; instead of just the top image, with the label showing up. I could also label the top image in a stack with flaga and, for example quickly delete all the image with an "X". Oterwise is seems the only option is to open each stack, by Ctrl-clicking the number in the upper left corner, that opens the stack; with all the images selected, then click the star lables I want to apply to all the images in the stack.
I don't remember where I found that plug-in. I'm hoping the guy who wrote it; and all I can remember about him is that he was from England, has written a version for Lr?