I've made some batch files for offzip/packzip which will decompress and compress the instance file with the proper windowbits value: http://dl.dropbox.com/u/37569004/rageunzip.rar
Just drag your save onto the correct .bat file. Strangely the instance file doesn't seem to have a checksum so you can just decompress, edit, recompress and it should work. I can't test them at the moment but I don't see why they wouldn't work. As for the profile settings, if you could upload your GPD then someone could take a look.