It depends a bit - generally, the files are in different subdirectories. This means that to move zone 30, you'll have to move all of the files with the name 30.something AND add those files to the index files in each subdirectory.
Of course, this isn't everything, either. Once the files are in the correct subdirs and indexfiles and thus loaded by the db handler, you'll need to connect the zones correctly, making doors/paths to the correct connection rooms using redit.
There's simply no easier way, using flatfiles. We might consider restructuring to another format (for instance a /zones/30/<all files for the zone here> structure), as that would probably be more easily swapped out and understood by the implementors. After all, back when the other system was made, there were fewer files per zone. But there's the matter of backwards compatibility to consider, so I don't think we'll be doing that.