Animal Crossing New Leaf – Who Can Visit the Island?

You can not have multiple save files of individual towns on the same 3DS system.

Every time you save your game it generates a new, random "Save ID" and stores that ID in both the SD/Savegame and the 3DS's system memory. Trying to load a save with mismatched IDs will result in being forced to wipe the save.

This prevents two things:

1. Having two towns with one copy of the game by using two SD cards.
2. Reverting to an older backed up save to undo changes you aren't happy with.

http://gbatemp.net/threads/question-about-id-checks-with-3ds-and-new-leaf-save-files.349216/

I have personally tested this (having purchased a 3DS and transferring to 3DSXL- my game was cleared since the save data and the system ID did not match). Prior to this, we attempted backing up the SD data, erasing it from the SD and attempted a new save file on the same digital copy. This also resulted in the ID conflict. I have contacted Nintendo on this matter causing an inability to back up data. I am yet to hear a followup reply.

In the case of mismatched IDs, the game will load with a "corrupted data" error. This forces the system to erase any save data associated with the digital download- and any backed up save file will no longer work for AC:NL.

If you have enough room in your town for new villagers (less than 10 villagers living in your town) you can force any neighbor into your town - so long as you know someone else who happens to have that villager, packed up and ready to move on their move date. If you visit the town the desired villager is living in, and go to the villager's home, there will be an option to tell them to move in upon talking to them.

As far as random move-ins, however, its totally random. However, I do believe if you have an abundance of a certain personality type, and are lacking in others, neighbors of the overpopulated personality type will typically be your "movers," and the personalities you have none of, or very little of, will begin moving in. Although this is just personal experience, as I do villager cycle in a diversity of different towns. I don't know if others have found this to be true as well in their towns.

There was a point that I had 5 Cranky villagers in my town, and every single day one of them would ping me asking to move. I had 0 Snooty villagers, and when I finally let one of the Cranky ones go, Baabara, the Snooty sheep came in. I then let another Cranky go, and I got a Lazy villager, Punchy, whereas I had 0 Lazy villagers prior to his arrival. Since then, whenever I don't force-move villagers, and I just rapidly cycle my town, I seem to find this pattern more and more true. The game tries to balance the personalities.

Hope this helps!

(The same goes for Campers - If a villager you'd like to have in your town is at your Campsite, and you have less than 10 villagers, simply talk to them a few times and they'll eventually consider moving in. Sometimes they'll just need to be persuaded by you talking to them a few times, but some campers can be difficult and will force you to win a "game" in order for them to move in. However, you can continuously play these "games" until they finally agree to come.)