Temporary Package Edits stopped working

In pre 2020 you could go into any package script and edit it. The edit would remain until you restarted Unity. I quite liked this because I could edit stuff temporarily to test / debug / explore without worrying about breaking changes.

But in 2020 it seems that if you do that, once you tab to the editor, Unity will instantly revert those changes which is annoying.

Is this something that can be disabled?

I actually have a workaround, which isn't ideal: Find the file in Explorer / Finder and make it read only. The problem here is that unity takes significantly longer to process any script changes. I think it's trying to overwrite that file but can't.

Making the package local wont work for me since it would add a significant number of files to my GIT repo, effectively blitzing my LFS.