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I am told compressed air (like... with a compressor, not the canned) and a nozzle work great for getting pesky grips off as well.To remove the current grips, sometimes you can just twist them off (though one hopes they're unable to spin, it does sometimes happen); otherwise you can try shooting some WD-40-esque liquid between the grip and bar to loosen it up.
I can ride in low 40's with a double insulated jacket, chaps, balaclava, timberland steel toes, and summer riding gloves. My hands and legs get pretty cold after my 1hr 20min commute though. A fully faired motorcycle also helps, as I wasn't able to do that on my old nekkid KZ.
I would really need heated grips, snowmobile gloves and cold weather pants to ride indefinitely. I've used my snowboarding gear before, but it looks a little goofy...