1. Disable automatic updates for Skyrim in the Updates tab of the Properties in the Steam games list. Or put Steam into Offline mode/Disconnect from the internet before starting it.
2. Don't open Skyrim at all, as Steam will then search for an update. The setting has some misconception, as people think it means "don't update" but it really means "Don't update automatically, wait until I try to play it." This prevents all your possibly hundreds of games from constantly updating whenever one has a patch.
This will keep Skyrim at 1.7. Then once the CK is updated to match, hopefully very soon, you may play/update Skyrim and use the new 1.8 CK to mod with Update.esm.
Hopefully you guys can see this before updating the game and being 'stuck' for a few days.

**This obviously can only save you if you haven't already downloaded the update. :/ **