How can I remove a rubber band from a pulley?
As I've said before in another answer, I find the #92585 Crowbar is the most versatile and is especially good at removing rubber bands from the #3736 (Technic, Steering Pulley Large) and the #4185 (Technic, Wedge Belt Wheel) elements.

Don't use any sharp/metallic objects like a screwdriver or a pen knife as you may scratch the brick or sever the rubber band.