This is a fantastic idea, just a simple config file which describes how to change a password for a site, which different programs can then interpret differently.
Thanks. Yeah; that's the idea for bootstrapping. At some point, I'd love it if sites themselves published APIs or at least manifests (similar to /robots.txt or favicon or a URL in a HTTP header, etc.) of how to programmatically change passwords.
A real problem I ran into is that a full browser is required for many operations, now. Instagram.com, for example, is completely opaque to non-DOM+JS browsers. Right down to the shamefully empty `<noscript>` block.