I'm doing all of these and None of it works out of the box.

Adding a field needs a default_db, otherwise old-code fails to `INSERT`. You need to audit all the `create`-like calls otherwise.

Deleting similarly will make old-code fail all `SELECT`s.

For deletion I need a special 3-step dance with managed=False for one deploy. And for all of these I need to run old-tests on new-schema to see if there's some usage any member of our team missed.