You might find a function like this one:
https://github.com/jkitchin/techela-emacs/blob/master/techela-grade.el#L149

helpful. There are some variations that do similar things.

John

-----------------------------------
Professor John Kitchin
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803
@johnkitchin
http://kitchingroup.cheme.cmu.edu



On Tue, Mar 5, 2019 at 1:51 AM Nik Clayton <nik@ngo.org.uk> wrote:

> Hoi,
>
> Is there an API for manipulating properties that are set in #+PROPERTY
> lines before the first headline of a file (i.e., not in a property drawer)?
>
> I've got some properties that (a) make sense when set for the whole file,
> and (b) the file contains multiple first level headings (which isn't going
> to change).
>
> Using org-entry-put when point is before the first headline throws a
> "Before first headline" error (when when the #+PROPERTY line already exists
> and I want to update an existing entry).
>
> N
>