We may distribute builtin providers which would be added to the registry db at startup. If later, a provider site makes their own implementation, their implementation should override ours.
pushed a fix for this in change https://github.com/mozilla/socialapi-dev/commit/3a731bfad4e4a861b17be5e3e0048f6e480dc143
While I did not add a flag, I do now store the manifest file location in the db, which will be used with bug 756590 in addition to serving as our builtin flag.
tests for manifest overwriting have been pushed.