I have a block of code that needs to run in multiple layers. So far I'm copy and pasting. That's bad enough. However, when I change the code I need to go through all the layers and make the change or re-paste it. A better solution would be to reference the entire block of code from a single location or an extra layer that just contains the code. Is that possible in AE?
Unfortunately, I don't think it goes beyond numbers and simple expressions. You can only use "thisLayer" as well--no referencing other layers. Plus layer names don't update as well as you'd like when you change the expression.
Another option is to use scripts:
Zorro the Layer Tagger combined with Expression Toolbox from aescripts.com