Keep an eye on the system status page at https://developer.apple.com/support/system-status/. As long as "Xcode Automatic Configuration" is down, that's likely to keep failing. Doing things manually should work.
> but can the breach allow attackers to upload modified apps in the name of the developer?
It doesn't look like they can. Uploading apps to the app store is done via iTunes Connect. That's always been a separate login from the developer center, and it has not been down during the current dev center outage.