Thank you @Rich Tener and team for the swift help. And thank you sincerely for your vigilance in protecting users against intrusion as well as insecure code. I'm impressed that you cross-posted to the geeknote forks as well as posting on this forum page. It's clear that you were striving for transparency and support.
To the Community: While I'm not the original author of geeknote, I've been maintaining an active branch at https://github.com/jeffkowalski/geeknote.
In the original source from which I forked, the consumer key and secret were checked into github, and since that can't be erased from the master record, that's a persistent source of problem that can only be addressed by disabling those credentials. I support Evernote's decision to disable access via those credentials.
As Rich points out, there is good news. We can generate and successfully use personal developer tokens immediately to regain access individually. Furthermore, moving forward there's the opportunity for a proper OAuth implementation. Please see https://github.com/jeffkowalski/geeknote/issues/89 for a bit more discussion.
In short, to get going again, it's sufficient to set the EVERNOTE_DEV_TOKEN environment variable to your own newly acquired developer token before invoking geeknote once again as usual.
For the longer-term solution, I solicit and welcome suggestions and coding help in implementing the proper OAuth solution that will make geeknote accessible again to users more broadly.
Please take those suggestions and pull requests over to the github site.