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Been spending a lot of time on here!
The folks at my local camera shop said that a plain old bottle opener will work to open the film canisters
You won't need anything to open the film cartridges if you don't re-wind the film all the way back inside it. When you re-wind the film, as soon as you feel/hear the film release from the winder side, stop re-winding. This leaves a few inches of film leader sticking out from the cartridge. Just trim it square and then load it right onto the developing reel from the cartridge (in the dark of course).
I prefered this method myself. You can use the canister to align the film with the reel - which can be challenging, esp with 35mm.