After being d.c'd every 5 minutes, I've come across a helpful tip for people who don't feel like exiting their client every time they want to switch accounts (Which is due to web log in update).
It is best to have a laptop with a internet on/off switch on it. Or, if you have any other ways to disconnect your internet you can do it like that too.
So heres what you do:
1) When logged in, click "Start Game"
2) When it says "Connecting to World", disconnect your internet.
3) Wait untill it brings you back to the log in page saying "Cannot connect to server".
4) You are now able to switch accounts!
Another way that Osayidan showed us
You can save yourself all the trouble of killing your connection.
Get: TCPView for Windows
Play mabi until you want to switch character.
alt + tab out of mabi, open TCP View
Find mabi, ctrl + click the mabi ones to get them all at once.
right click --> close connection
mabi get's disconnected as if you had pulled out your LAN cable, while everything else is fine (ex: MSN or your downloads won't stop).
That's the lazy way to do it.
A 3rd way (Much faster than the first way).
1) Disconnect Internet
2) Hit back
3) Log in