For version 10, user Tuto has a nice post here Run Multiple Instances of Yahoo Messenger By Tweaking Windows Registry.
For version 11, derived from this tip, I tried on Windows 7 and come up with the below tip as just making a minor modification.
- Run `regedit`
- Go to HKEY_CURRENT_USER\Software\Yahoo\pager\Test
- Add new value `plural`, details:
- Right click on the right pane, then New – DWORD
- Rename it to `plural`
- Update `plural` value to 2, details:
- Double click it
- Enter 2 in `Data` box
- Select `Heximal` radio in Base box
- Close `regedit` program.
Note: This worked on Windows 7 and I’m not sure other previous Windows version. Please contribute with me if you did try.