Copying realms is just that - a snapshot copy at that point in time. When you copy a realm, it is not added into another realm. The original realm BECOMES the new realm. Think of it like copying a file on your computer. There is no merging of information.
If you want your content to be merged and evolve, then you'll need to use the export and import mechanisms. When you export content, we track the original source of each piece of data, and we preserve that when it gets imported. So when you import updates to that content, we can detect it and merge everything together.
If you are dealing with purchased (i.e. secured) content, then that content won't be varying. It will be the same content every time that you bring it into a realm. So you can import that content into multiple realms and get the identical results each time. Consequently, if you copy a realm and later purchase new content that you want in both, you can simply import it into each of the two realms.
The only limitation of all this is when you want to import a bunch of purchased content, mash it all up, and re-use the mash-up in multiple realms. In order to do this, you'll need to copy the realm, since export won't include all the purchased material. However, if you then want to continue evolving the first realm and duplicating those changes into the second, you'll be limited to only your own new creations at that point. Any purchased content you bring into the first realm will not be exportable and re-importable into the second realm, so mash-ups of subsequently purchased content won't export cleanly. That being said, you can always independently import new material into the second realm.
This limitation is a by-product of needing to ensure that secured content cannot be freely copied via the export mechanism. It's also only an issue due to the use of export/import to handle all this stuff. Once we have all this logic orchestrated entirely through our server, these constraints disappear. We're still working towards all that, since that was our original vision and design. We instituted the export/import solution as an interim step along the way.
Hope this helps!
