How do I safely handle/open a glass canister of butane?

Outside in the open air - carefully. Welcome to A2K. BTW, in another life, I used to smoke, and also used lighters. I would suggest you go to the local tobacco shop and ask them the best method to refill your lighter with butane. You can even call them on the telephone. Better safe than sorry.

Here's a link on a butane lighter that may provide some clue on safety.
http://www.cpsc.gov/cpscpub/prerel/prhtml73/73042.html

Put it in the freezer, first. I've had backpacking trips so cold, there wasn't enough pressure to flick my bic without warming it up first with body heat.

Roger - that's why propane (boiling point of -43.67 F at one atmosphere pressure) is normally used for fuel. Unless you're in the Antartic, it's unlikely you'll run across temperatures that cold. Field butane (a mixture of normal and iso-butane) boils at around 25 F, and it's not unusual to be out in weather that cold in the winter.