If the data is in clear text a password does absolutely nothing to prevent
someone from using a utility to change the password block on the tape to
turn it off.  Now, if it is encryption, TSM can do that.  You can not
restore the files without the encryption key.  However, this is only 56 bit
encryption, though much better than a password.  It also happens on the
client before the data is even shipped.  There is a limitation, the TDPs do
not have the encryption support.

Now, I do not know if you know this or not, but TSM does not write out tar
files like NetBackup.  Finding the data on a TSM tape without a database is
very difficult, but can be done.

I would be helpful if you identify the business requirement you are trying
to solve here.