Alt-Replace

Alt-Replace lets you swap out one item for another across selected comps or all the comps in your project at once.

Simply drag the item you want to replace from your project panel into the first dropzone, then drag the item you'd like to replace it with into the second drop zone.
Alt-Replace will run through all your comps (or just your selected ones if you clicked that option) searching for the first item and replacing it with the second.

It's just like when you usual Opt/Alt replace a layer, except across all your comps at once.

Installation

The easiest way to install Boxer is by using a ZXP installer, like the one available on aescripts + aeplugins; https://aescripts.com/learn/zxp-installer/
Once installed, restart After Effects and Boxer will be available within Window > Extensions > Alt-Replace..