What do you mean by adding multiple library?
Will it mean adding multiple Libraries to Library list as soon as you login to system under initial library list.
For adding the libraries to intial Library list, You will need to change the User profile.
By using CHGUSRPRF command, and then by taking F10, You will find the below option
<pre> Job description . . . . . . . . JOBDNAM Name, *SAME
Library . . . . . . . . . . . LIBNAM Name, *LIBL, *CURLIB </pre>
and by using CHGJOBD command, taking F10, you can change the initial Library list.
You can add you your own libraries along with system Libraries.
<pre>Initial library list . . . . . . LIBRARY1 Name, *SAME, *SYSVAL, *NONE
This Library lsit will appear in your library list as soon as you login.