3 of 3 Single-letter typo fixed.

GNU tar has a --delete option that works with archives too nowadays.

Use it like this, for example:

tar -vf yourArchive.tar --delete your/path/to/delete

Beware: It will most likely not work on any kind of magnetic tape medium. But tar has no problems working in a pipe, so you can just use a temporary tar file and overwrite the tape with that afterwards. It also won't work on compressed files, so you would need to uncompress the file.

Also, the operation will be rather slow in any case, due to the (by design) packed linear nature of tar archives.