You should be able to reload it in the dark. Just put it into the back as you would normally with the white tabs where they should be, close the back and you'll be good to go.

Also, if you break a white tab off you'll have to go in the darkroom, pull out that sheet manually and send it through the rollers manually, then close the back and as long as the rest of the white tabs are where they should be, it will work for the rest of the pack in the same manner.