Control the opacity of dozens of layers via a dedicated “null” (no precomp, no one-by-one pick-whip)

[Matthieu2405484496h8]

In one comp I already use Null A to drive the size/scale of a group of elements. I also need a Null B to control the opacity of many layers (bars, logos, etc.) without:

• pre-composing those layers, or
• pick-whipping opacity one by one (sometimes 50+ links).
  Ideally, I could bulk-link multiple layers’ opacity to a single controller (null/effect controller), with a quick way to (re)connect/disconnect layers, and have it coexist with the existing parenting for Scale (a kind of “multi-control”: parenting for Scale + global controller for Opacity).
  An explanatory video is attached to the ticket to show the current setup and the desired outcome.

video explanatory and desire result 

[ShiveringCactus · Accepted solution]

Set up one layer.  Then copy the opacity property (CTRL + C).  Highlight the other layers and paste (CTRL + V)

[H34186713qx8p]

This doesn't work

[ShiveringCactus]

Really?  I still works for me.  You have the opacity and its expression all set up?  Then you copy it and block paste it to all layers and it doesn't work?  What happens if you do it to just one layer?  (As a test?)