Context
Reasons you might want to change the upstream on an existing project vs starting a new project:
- billing is already set up, and a hassle to redo
- site IDs are in use in CI like Travis
- lots of users are associated with the dashboard
- the site is part of another organization and needs to stay that way
Terminus
If you are looking to remove the default upstream from a fresh Drupal/Wordpress site, you can run the following Terminus command:
terminus site:upstream:set my-site-name empty
Hacky Solution
WARNING
DO NOT DO THIS METHOD. IT IS OUTDATED. This method will completely blow out your database and your ENTIRE commit history on ALL Pantheon environments. Be sure to back everything up!
Backing up
Make sure you have a local copy of the codebase via git. You can use this to rebase against the new git upstream. See Creating Pantheon Sites and Choosing an Upstream under Syncing remotes on how to replay history from one remote over top of another.
Export your database from the dashboard and download it locally. You'll want to re-import it later.
Changing the upstream
Visit your pantheon dashboard
replace #dev/code with /upstream and reload the page. Voilà you are back at the distro selection screen and can re-install.
note that if you are importing a database that defines the standard installation profile for the site, but are moving to a distro like Panopoly (or vice versa), you'll need to take some extra steps to rectify the system table and more.
you cannot specify a random upstream on github. New upstreams need to be Pantheon-approved via a ticket in our organizational dashboard.