But it's genuinely what we were all doing not so long ago

Jokes on you, my first job was editing files directly in production. It was for a webapp written in Classic ASP. To add a new feature, you made a copy of the current version of the page (eg index2_new.asp became index2_new_v2.asp) and developed your feature there by hitting the live page with your web browser.

When you were ready to deploy, you modified all the other pages to link to your new page

Good times!