I've done it warm. Is it an auto or manual? If it's a manual, then Honda just recommends a simple drain and fill. I believe automatics require a flush, but feel free to correct me if I'm wrong on that!
A word to the wise on tranny fluid, stay away from ANYTHING other than Genuine Honda fluid, manual or automatic. That's part of the problem with the auto trannys blowing even after the recall has been performed. Hondas tend to be finicky on fluids. An independent spe******t once told me he would only put non-Honda engine oil and brake fluid in his personal car.