I recently wanted to rename a model and its postgres table in a Phoenix app. Renaming the table was simple and documented, but the table also had constraints, sequences, and indexes that needed to be updated in order for the Ecto model to be able to rely on default naming conventions. I couldn't find any examples of what this would look like but was eventually able to figure it out. For anyone else in the same situation, hopefully this example helps.
In the example below, I'm renaming the Permission model to Membership. This model belongs to a User and an Account, so it has foreign key constraints that need to be renamed.
defmodule MyApp.Repo.Migrations.RenamePermissionsToMemberships do
use Ecto.Migration