LABEL Tapes with different volser

I have trouble labelling tapes on TSM, if those tapes has already been initialized with a different volser.
Using Library Managed Encryption, if I change the external label of the tape and then try to TSM-LABEL it, it fails with I/O Error. To obtain my goal I have to label it without encryption (keep the new volser outside B.E.P.) then label it again with encryption enabled (inside B.E.P.).
I would like to do the work one time... without changing Barcode Encryption Policy.
Any idea??
Thanks for any suggestion