Calling an expression that's stored in one place (like a link, or an "include")

I would like to make an expression (for use on various layers throughout multiple comps) that triggers a main expression that's stored in one place.. (maybe this would be an expression on a layer on some unused dummy comp or as a text file, if possible).

In terms of programming this is like using an include file.

Is something like this possible? The purpose is to allow editing all the instances from one place.

Thanks