[PeterisP]

It's feasible to make such a tool to update the database schema so that it would match a changed definition, but I don't think that it's feasible for it to update the actual database.

To do that, you need knowledge about how and why the schema was altered, and schema definitions like protobufs or graphql don't contain that. For example, how would you distinguish between renamed column (where you need to keep the data) and deletion of a column plus adding a different one?

There's a reason why migrations are the standard level of abstraction, packaging changes to schema with scripts ensuring consistency of data throughout the whole version history.