Yup, that's been done... I think... I'm sure, I used Joshlog, rompatcher and xplore to do this, and I have no trouble with .mif patches/skins for other widgets, for example the steel mail widget is a .mif and works great.
This is different, at least it seems like it to me. These are .nvg files not .mif and they are to be "add to theme"