editors/tweak - The NetBSD Packages Collection

tweak is a hex editor. It allows you to edit a file at very low
level, letting you see the full and exact binary contents of the
file. It can be useful for modifying binary files such as executables,
editing disk or CD images, debugging programs that generate binary
file formats incorrectly, and many other things.

Unlike simpler hex editors, tweak possesses a fully functional
insert mode. This is not useful when editing many of the types of
file described above, but can be useful in other situations. Also,
an insert mode makes it easy to use tweak to construct new files
from scratch.