tar-chgrp-entry
tar-chgrp-entry is an interactive compiled Lisp function in `tar-mode.el
'.
(tar-chgrp-entry NEW-GID)
Change the group-id associated with this entry in the tar file.
If this tar file was written by GNU tar, then you will be able to edit
the group id as a string; otherwise, you must edit it as a number.
You can force editing as a number by calling this with a prefix arg.
This does not modify the disk image; you must save the tar file itself
for this to be permanent.