Paradox always attempt to make new patches save-game compatible with the previous one, but it's not always possible and is virtually never 100%.
You should also copy your whole CK2 directory structure out from under Steam to elsewhere; that will work fine without Steam running and won't be patched. You'll need to use the userdir.txt trick (see the sticky "file locations" thread above) to not have it use the same save games and settings as 1.10 when it does come down.