For those worried about your mod list getting broken again with this new shovel-full of creation club content, or worried about mods that devs have long ago walked away from becoming permanently broken, I have the cure!

Well...I have a palliative.

First: Right click on game > manage > updates. Set it to only update when you play it. This will prevent it auto-applying the update when it goes live.

Then: Click "Games" at the top of your client, then use the "add a non-steam game to my library" function.

Use the "browse" button, find the game's install location, then pick the Fallout4 executable. If you're running Script Extender, it might be f4se_launcher or something like that.

A new entry should show up in your Steam library. Moving forward, launch the game using that instead of the normal game button. This will prevent updates while still allowing steam overlay to function.

Just be careful never to launch the game using the original button and you should be fine assuming your install never borks out or something funky happens with the steam validation in the distant future.