I pop factory loads with a two sided bottle opener. I also tend to fold and tear off the tail of the film as well. I've had some films come out with adhesive residue which shows as an unfixed pink blotch of goop on TMax films. I'm very leery about sharp objects in my dark bag lest I puncture or cut the fabric by mistake, so I have no scissors, and the sharp end of the bottle opener is blunted with a chunk of rubber tube.
As far as identifying used cassettes, I bend the leader back on itself to show the film as exposed. There's often little time when shooting an event to trim the leader nicely.
Has anyone found a better tape as far as adhesive residue than vinyl electrical tape for sticking film to spools when bulk loading?