For e.g. changing the format of a column that's easy enough but it's tricky to create that intermediate state at the migration level for every migration. One option is to deploy the migration code without restarting the running services (or to a different box), rollback the code if the migration failed, restart the services to pick up the new code if it succeeded. This still means not writing migrations that actively break the running version though - if you're using database reflection, everything will go boom when the schema changes.