I don't know how exactly these work, but what you may be looking for is Trazlander's magic blocks. The general idea of them is that spawning minecarts spawn in falling sand entities in a certain way with certain IDs, so that when they land, they turn into a certain type of block and make some type of building or device. Then you can make these disappear by turning them into falling sand entities again, and have them fall on half slabs and disappear. Here is a video that explains them (by Trazlander himself):
You will need MCEdit to bring the magic block spawners into the game, but you won't need any mods once you go into the game. Here is where you can find the MCEdit filters for them: http://elemanser.com/filters.html
Trazlander has a tutorial on how to use these as well:
Each player has their own file in a world's playerdata folder, named by their UUIDs:
These files contain their inventory, location, health, etc.
Note: If it's an older world there may also be a players folder with similar files. Ignore this, it is obsolete and does nothing.
In addition to this storage location, on singleplayer, the player's data is stored in level.dat, always under the name "Player". This file contains other data, and you need to use the editor NBTExplorer in order to view contents and manage the data:
On singleplayer this default "Player" version takes precedence. If it exists, it will always be used first, and it doesn't care who the user is, so long as it's singleplayer. Both of these locations are saved to with your current in-game data.
This means that you can play a world on singleplayer with one account, then give it to a friend (or upload it to a site) for other people to continue where you left off (still on singleplayer), it will use the Player file rather than the one specific to your UUID.
As LAN worlds are created by first launching singleplayer then opening the world to LAN, this Player data in level.dat will be the data of the host, Player A. As you are now opening the world on singleplayer (before opening it to LAN), it is using the data of the Player file, or Player A's data, rather than your own UUID file.
This also means that the data for your character stored in the UUID file has probably been overwritten with Player A's data. Everyone else still has their own UUID file intact, as they've only logged into the world while it is on multiplayer.
To fix this, you'd first need a backup from before the transfer. In level.dat, delete the "Player" section and then log into the world on singleplayer. This should force it to load your UUID file and then re-create the Player section in level.dat based on that, rather than the other way around. Everything should work fine from there.
Best Answer
The proper way to do this is to host a server. If you're in the same local network (which a home network usually is), then it's pretty simple, you can skip most of the steps in the tutorial (archive) and just download the server, put it into a folder where you want to have all the server stuff, run it once with
java -jar server.jarin a console (after switching to that folder withcd), change "eula=false" to "eula=true" ineula.txtto agree to the usage terms and you're done with the initial setup (and you can move your existing world there, modify settings, etc., if you want).From then on you can always just start the server with the same
java -jar server.jarcommand, which can be put into a desktop shortcut or similar, if you want.On Windows, you can assing Ctrl+Alt+[key] key combinations to shortcuts, if you put them into the "all programs" folder of the start menu. On pretty much all Linux systems you can just bind keys to any console command directly.
When the server is running on a computer in the local network, it automatically appears in the "multiplayer" menu of Minecraft. You can also add it as one of the servers that are always in your list, that skips a few seconds of waiting until the server is discovered by your game.
The hacky way: You can automate clicking the buttons or running
/publishusing a click/keyboard macro. On Windows, I can recommend "TinyTask", on Linux "xdotool" or maybe "cnee", some people also like "AutoHotkey".