I just tried and it didn't work I had a problem while saving though, it said I wasn't allowed to do that. What I did was save the file to my desktop and then move it to the CAW folder and replace the original Default file but maybe it's not that easy? it still says it's not compatible.
Edit: the tools section of the official website is down si I'm hoping that means that the new version we'll be out soon.
First of all, DO NOT copy the whole default file, just EDIT the little paragraph at the end.
GameVersion = 1.36.45.017001
CompatVersion = 17
WorldBuilderCompatibilityVersion = 14
ONLY change the figures 17 and 14 in CAW to match whatever you have in the SIMS original folder (Not the EP folder)
Here is a little edit that I over looked...Use the information from Default file from 'The Sims Original' folder, that is, C:\Program Files\Electronic Arts\The Sims 3\Game\Bin. Use that information to replace the information from the Default file in CAW.
I believe your computer settings does not have the required permissions to edit systems files, that is why you couldn't save. But I don't want to cause complications for you. That's the method I use each time I install a new patch until EA releases a new version.
So, you might just have to wait for an official update. Sorry.