Arbitrary Editor for Mac
This seems to be the job for a hex viewer/editor rather than a text editor. An easy way to do this would be just to use Terminal emacs with hex mode.

If you prefer a GUI application Hex Fiend looks promising


  
  A fast and clever open source hex editor for Mac OS X.
  Insert, delete, rearrange.  Hex Fiend does not limit you to in-place changes like some hex editors.
  Work with huge files.  Hex Fiend can handle as big a file as you’re able to create.  It’s been tested on files as large as 118 GB.
  Small footprint.  Hex Fiend does not keep your files in memory.  You won’t dread launching or working with Hex Fiend even on low-RAM machines.
  Binary diff.  Hex Fiend can show the differences between files, taking into account insertions or deletions.
  Data inspector.  Interpret data as integer or floating point, signed or unsigned, big or little endian...