very simple and easy trick ..
Go to Start Menu> Run > Type Regedit
Look for HKEY_CURRENT_ USER
– Software\yahoo\ pager\Test
There you may find only one registry named “Default”
– Right click in that area Click New > Dword Value
– A new registry will appear there.. Rename it as Plural > Right click > Modify > Set the Value Data 00000001 and click OK
Open another Yahoo Messenger and Enjoy logging with another ID