If you have several yahoo messenger accounts and would like to use several instances of the yahoo messenger program, which by default is not allowed, you can use a very simple trick, and transform your yahoo messenger with one single line of code entered into the command line into a veritable yahoo multi-messenger.
Make sure your yahoo messenger is NOT running, that is, it’s not merely closed and hidden in the tray, but actually removed from memory.
Right-click on the yahoo messenger icon in the system tray if your messenger is running, and select “Exit” from the context-menu that appears.
Confirm that you want to exit.
Fire up a command prompt – or cmd window – by holding the WindowsLogo button on the keyboard, and pressing R. Type “CMD” and press Enter.
Then copy and paste [ or watch and type 🙂 ] the following command EXACTLY as it appears in the next row:
reg add HKCU\Software\yahoo\pager\Test /v Plural /t REG_DWORD /d 1 /f
and press ENTER after it.
There you go, you don’t even have to log off or restart, you can simply start now several instances of yahoo messenger.
I have personally tested this on Windows XP, service packs 2 and 3, and on Windows Vista and Seven, with Yahoo Messenger versions 7 and above. On Windows 7, you migh need more time or accepting the modifications made to the registry, when the popup shows that you need to approve the changes made, but nevertheless, it still works.