I haven't tested Adobe Bridge yet, but you can find some tag information from Lightroom 4.4 here
LR uses xmp:rating
for the rating, so to clear that your command would include -xmp:rating=
or to clear rating data that might be in the EXIF block as well, -rating=
To clear the label, use -label=
You can add -P
to prevent the system time stamps from changing and the ModifyDate
tag isn't automatically altered by exiftool, you have to do it manually.
To set rating and label, you simple set them equal to the value you want. For example, -label="Approved"
to set the label to Approved. You may have to play with what values rating sets and reads. I haven't tested to see if it's a 0-5 scale or 0-100 scale.
See FAQ 3
for help in figuring what Bridge reads and writes.
Bridge is on my list of apps to test and chart like I did for LR, but I haven't gotten around to it yet.