With NetBackup, there is no need to format media. The first time you write to a tape, NetBackup will write header information that includes the MediaId. The MediaId is the way NetBackup identifies media.
When you run bpexpdate, you are not modifying the contents of the tape. Instead, what you are doing is removing entries in the Media Manager database about the contents of the tape.
If you remove media from a tape library and put it back in, NetBackup will treat the tape the same way. The only way to get it to treat it as a new tape is to first use bpexpdate to expire all images on the tape (image = the output of a backup). Then use the bplabel command if you wish to change the MediaId of that tape. Otherwise, the MediaId remains the same.