I personally don't see the point of tracking changes; you're going to have to unarchive and archive each map anyways. It might even be harder and take longer to track just the changes, when you could just overwrite the old map with the new one completely.
The point of the change list is that there's no map to archive/unarchive in the first place. Memory becomes significantly less of an issue when you're *only* storing the blocks or chunks the player has modified.
*Chunks would be more memory efficient