Awesome writeup! Validating to see that the way I do it is the way stripe does it with bajillions of records, while the system is running. Very pragmatic and incremental - maybe a little overly cautious with the feature flag, but better safe than sorry.<p>I&#x27;ve had to do similar when migrating password schemes. When users login they would validate against their current password, and then generate a new password hash to use next login. Although these types of migrations usually take quite a while, as a user has to login for the migration to happen.