The EMC Assignment GUI is the configuration utility inside EER for custom EMC values. Values set on singleplayer worlds will be global to all of that client's worlds. However, values set while opped and connected to a server will be transmitted to the server and sent to other clients. If a client with singleplayer EMC values defined connects to a server that also has custom EMC values, the server's EMC values will be loaded without overwriting the client's EMC values.
Using the GUI Edit
To pull up the GUI, get an Assignment GUI Activator out of creative mode or NEI. Right-click it, which will bring up the GUI. Next, choose the item that you want to search for, either by searching in the field or by just scrolling through the list. Edit as many items as you like this way, and then hit "Done". This will close the gui.
Sharing Settings Edit
Custom EMC values you create with the GUI live in the config/eer/emc folder. If you want to share this with somebody (though your configuration will propagate automatically through a server), just copy this folder and have them paste it into their config/eer folder.