I checked with the team and the feedback is that this isn’t really supported anymore, resin in 2013 was a very different beast from what it is today – they also reitterated that swap on media like an SD card is not a great idea, especially in production.
That said if it’s critical for your use case, you could look at https://github.com/muchlearning/make-swap/ and see if it works.
I’ll also update the blog post and add a deprecated note to it – thanks for bringing that to our attention