It depends on the file…
If it is a cr2, pp2, dsa, ds, etc any text editor will work (notepad, but it is very limited…Notepad++ is a favorite alternative)
If it is an uncompressed dsf/duf, the same thing, any text editor.
If it is a compressed dsf/duf, it will need to be decompressed or edited within DS. This also goes for any compressed Poser files (ppz, etc)...decompressed first. Something like the command line version of 7zip should work to decompress the files. Or there is a way to do it from within DS (for Daz format files) or Poser.
Another way, but one that isn’t very easy…for Windows, is to use a text editor that can edit compressed files on the fly. The setup usually involves setting up the text editor, because I haven’t found one that doesn’t have to use some sort of plugin that needs to be configured before it will work (that’s where the complexity lies).
Also for DS there is the DSFToolbox.