I know that using an underscore in front of a custom field name hides it from display on the front-end, e.g. `_custom_field_name`. In my experience, WordPress also prevents one from adding such a custom field on the front end.

Before I go spelunking around core, I wanted to ask: Is there an "easy" way to allow `_custom_fields` to be added from wp-admin/post.php?

The reason is this: we rely on hidden custom fields, but when troubleshooting production issues in prod it would be useful to be able to inject certain hidden post meta. I'm not a fan of touching the production database by hand. 

![what i get](https://i.stack.imgur.com/tD1Ym.png)