Why should it crash? If you simply erase all the saved data and then convert it to CoreData database - you most certainly won't face any crash.
There is a thing to note here - this might not be the best way to solve the problem. Also read about CoreData Versioning
mechanisms as they will save you from fails in updates later on.
You can also hypothetically test the behavior of your app like this - download it from the AppStore, launch it and do things, then use Xcode to install the new version on top of it and see what happens.