|If the question in fact meant "Can I replace a SCSI connected tape drive without powering off the server ?" then the answer is:|
Don't do it, except if the connector/mounting bay is of the "hot plugguble" type, I doubt that a tape drive is of this type.
Said that, if You really take the risk, be aware that there can be errors in I/O operations on disks connected to the same scsi bus.
After replacing the drive, it has to be made known to the system using the "IO AUTOCONFIGUE" command in SYSMAN, unless the system is rebooted.