Not really an answer, more the tacking on of another question:
I've been doing this through the rest api using the items resource with the /data addition. Not sure where this last part is documented.
GET https://myPortal.net/portal/sharing/rest/content/items/fd1f7cb22b3f467fabb0a319bcf1a5e9/data?f=json
Using the dashboard ID returns the json, but I don't know how/if you can make changes.
Where I get lost is in the json layout. I'm trying to use it but it's inconsistent across dashboards and so modeling it is not possible. I'm searching for some docs describing how it's laid out, but so far I've not had any luck.
