Chances are you have more than one (1) yahoo ID, and you are tired of signing in and out whenever you want to use the other. And you want to do this in three simple steps.
You came into the right place…
Here I will post the step by step guide / how to do this in windows.
Step 1:
Go to Start->Run then type regedit, click ok.

a new window will pop up named registry editor
Step 2:
Go to folder software->yahoo->pager->test
Right click on the right panel click new->DWORD value

A new file will be created.
Step 3:
Rename that new file as Plural.
after renaming double click to change its value to 1.
Now your ready to use YM simultaneously with diff Yahoo ID, to doso sign in as long as you like, as many as you like, as long as your computer memory permits you
.
ENJOY…
