Not OP but here what we have is some routine to get a fact from the DB (eg Customer->getOrders()) and the routine is schema aware. On v0 it queries a table with one rules, on v1 it's a different slightly different query. So, one small schema mod to eg add a column. Roll out. Another schema mod to populate, possibly a few days later, then roll out queries over a few days, then, later slowly remove the dead parts of the schema and then later drop the legacy code using the old columns. The process can take weeks. And some throwaway code (scaffolding I say) has to pass through the system. I recently was able to clean up and old view that took months to process through (we're a small team)

One recent one was moving from bitflags in an int column to flags in a jsonb column. Tedious.

What makes it work? Testing, testing, testing and management that gives time for that process.