Minecraft 1.8.2 is coming out in a few days and they said there will be NPC villages, strongholds etc. I built a massive city on the Xbox and I really want it to have villages, strongholds and all the new features. Is there any way I can keep my world and play creative mode and have villages and strongholds in the same world?
Until the update is released, it's not 100% certain, but probably (sadly) no, you cannot.
You will get access to many of the new features, such as Endermen, enchanting, creative mode, etc. But probably not the terrain-related features you mention, such as Strongholds and Abandoned Mineshafts.
The reason is that these features are implemented by changing the terrain-generation algorithm. On the PC version, this means that new terrain features only appear in new chunks, generated after the update is released. But in the XBox version, worlds are generated all at once, on world initialization.