Is there a way through either AMPScript or SSJS to manipulate custom content inside the email sends through the Marketing Cloud? For example, say I want to add information for 'List-Unsubscribe' into the header to allow for an automated unsubscribe process, would I be able to do this using server side code on the email?
Everything I have seen referenced in the SSJS and AMPScript functions does not seem to mention any capability of this, but thought I could ask as maybe I am missing something.
If I cannot add through scripting, what would be the best way to approach having this added in?