The way that you'll run multiple parties through the same realm is by entering the realm data once and then "sharing it" privately with yourself. Once it's been shared, you'll create two new realms and import the shared realm into each of them. At this point, the two new realms have copies of the original and can be played out independently of one another.
Everything here is designed to run through the sharing mechanism, since that way we can handle all the different ways users will want to use this. If someone is running two parties through the same realm simultaneously, he can do so. If someone else wants to run one party through the realm and then another at some later date, he can do so. Etc.
The critical detail here is that we need to having the sharing mechanism in place for all this to work. We don't have that ready yet.
If, after reading this, you still want the ability to do a full reset of a realm to nothing being revealed, that's definitely something we can do. Please post the request on the Feature Requests forum where other users can find and up-vote the request. That will help us prioritize this feature relative to everything else we have planned and that users are asking for.