I like to restart a lot when I play minecraft; and I rarely play online. I am the kind of player who will start a game, get established, explore, and then get bored and start again. However, I like the idea of starting all my new games in the same world.
I found that if I replace the 'region' folder in one save folder with a symbolic link (or a 'shortcut' in windows) to the region folder of another save, then they both save to the same location, and changes in one game are reflected in the other; but world generation anomalies tend to occur, due to multiple different seeds being used depending on which game is used.
Further, I found that if I linked two games with the same seed (e.g. one that was re-created from the other), then each would act like its own game, as above, but without the problem of world generation bugs. The only downsides seem to be that I have to start and respawn in the same location each time (the global spawn for that seed), and that it is tedious to set up each time I restart.
Additional notes: the 'linked' games allow for individual games to occur as if they are different users on the same server; they have different coordinates, inventories, and ender chest contents, but the world is the same.
To the Question
I would like to be able to start new games in (ideally a new location in) a pre-existing world, while having the old game still usable. If there is some kind of mod or third-party package which I can install to automate this for me, that would be really cool. If not, if anyone else has tried and succeeded at this, I'd like to hear your solutions.