Re: Expressions to apply adjustment over multiple comps?

This should work. Link the effects back to an Adjustment layer in a comp named Control, then make a preset so you apply the setup easily to new or existing layers.

Make a comp named Control. Add an Adjustment Layer. Add the Effects you want to control. I used Remove Grain and Color Balance when testing.

Now's the tedious part. For every parameter you want to control in the other comps, we need to link them back to the Control Comp, but we really only need one since we can make a preset from that, then apply it anywhere we want.

In one of the comps to be controlled, click an effect, say Remove Grain,
then twirl down and Alt_Click the parameter you want to control, I opened Noise Reduction setting to get to- Noise Reduction. Alt_Click the Noise Reduction Stopwatch, then pickwhip (looks like an "@", middle of three boxes) to the Noise Reduction of that Adjustment Layer in the Control Comp. You'll probably need to pickwhip to the effects palette or drag the comps apart in the timeline. Anyway you get an expression like this:

comp("Control").layer("Adjustment Layer 1").effect("Remove Grain")("Noise Reduction")

Do that for all effects you want to link, like for Chroma Suppression:

comp("Control").layer("Adjustment Layer 1").effect("Remove Grain")("Chroma Suppression")

I did it for all ten stopwatches in the effect, Color Balance.

When you get one of the layers completely linked back to the controller via expressions, then select the Effects in that layer you want to make a preset of, Remove Grain and Color Balance in the test, then click, Animation>Save Animation Preset... give it a name.

You can now apply that preset to any layer you want to control with the Adjustment layer in the layer named Control, and the effects will be applied, with the expressions to link them up.

Unfortunately, there is one little catch, some effects even though they have stopwatch cannot accept expressions, like Levels and Adjust Hue Saturation, so it's a no-go for those.