View the original community article here
Last tested: March 2021
The only way to have Looker generate LookML for you is to create a new view generated from a table, or to add a query to LookML from SQL Runner. From there, you'd pretty much copy what you wanted from the generated file into your existing file, and then delete the new file.
Another idea (which sounds good in theory, but may be too complex in practice) is to have two views: a base view that is just auto-generated LookML, and another view that extends the base view and makes desired changes. This way, you can just re-generate and obliterate the base view whenever you know your database changes.
There is a feature request for this functionality here: https://portal.feedback.us.pendo.io/app/#/case/17638