I just found the term I'm looking for:  "advice" -- here's an unrelated
example:
https://emacs.stackexchange.com/questions/17169/change-order-of-buffers-in-helm-buffers-list

On Wed, Aug 14, 2019 at 3:36 PM Nathan Neff <nathan.neff@gmail.com> wrote:

> Hello all,
>
> There are quite a few commands I run in org-mode to jump to
> headlines:  org-clock-goto org-capture-goto-last-stored, etc.
>
> Sometimes, I would prefer that those "jump" commands would use
> a new window to perform the jump.
>
> In my quest to learn Lisp a bit better, I'd like to ask for recommended
> way(s) to set some kind of flag "e.g. use-other-window", and "wrap"
> the various jump commands with code to switch to the other window (or
> create one)
> and then call the function.
>
> For example, something like:
>
> (def decorator njn-switch-or-create-window() )
> (if use-other-window ( switch or create window))
> (call original function)
> )
>
> (decorate (org-tags-view, org-clock-goto, org-capture-goto-last-stored
> njn-switch-or-create-window
>
> I *know* Lisp has a bunch of ways of doing this, but I would
> like to hear the "best" way to attempt something like this :)
>
> Thanks,
> --Nate
>
>
>