Yes you can cut the top, but to be honest, it would have been better to do it in August, early September. As the weather's chilly, you may find the tips you've cut do go brown.

bamboo is very tough as plants go . it will soon regrow new canes even if you cut it to the floor . i cant see why youd cut the tops out as that just makes the plant come back just as tall if not taller with a vengiance . id be inclined as i do myself to dress it ie cut out and thin the thinner canes and all the lower leaves and it will show more light threw etc . this does depend on what bamboo you have .