It wouldn't mess up the victim's game but the other person would like turn the entire dream town into their own, right down to even the player characters. I don't remember the details (and probably couldn't discuss them here) but it had to do with cheats, not a save editor or anything like that. I don't know if hacked Switches have reached that level of access yet but they probably will eventually.
Yep, it happened to me with my AHS town. It was very upsetting, and I pretty much stopped playing New Leaf after that.
That would be really cool, actually. I'd love to tour one of the developer islands!Probably the official Nintendo DA. They had one for NL. And it will probably have more goodies since they can just put them in. Who knows maybe someone will be able to find something that hasn't been updated in the game yet but the official Nintendo island has.