I had success (back in Simpana version 10) using this command:
E:\Program Files\CommVault\Simpana\Base>SetMediaLocation -filename SML1.txt
where SML1.txt is a list of lines of this form: barcode <tab> newLocationName
Now we have CV 11 SP4 and I no longer see the SetMediaLocation.exe command.
What I will try next is described in the next link but it appears I'll need a script to call qoperation 4000 times to move 4000 tapes. This may work but seems inefficient.