Short answer: Yes! Long answer: When you launch the game after installing EW you get a choice to fire up with EW or EU. I haven't tried the EU option since I got the expansion so not sure if anything got tweaked. However, I do not believe the current version of Toolboks will make any changes to EU. Both games have their own folders and executables, and Toolboks is currently (to my knowledge) only set up to modify EW. That said, EW simply added things on to EU. If you play through EU, when you get around to playing through EW you still have to do the same campaign/story, which isn't a problem if you like multiple playthroughs but if you're the sort who gets bored replaying the same story it might not be optimal.