Bring it inside to work on it, then, back out it goes.
Please be aware that trident maples are a little more sensitive to the cold than other maples. The top parts are ok with the cold, but the roots don't do well if they get really hard frozen. Set the pot on the ground, and mulch it in really good. Some I know use a type of heating pad to keep the ground a little warmer for their tridents. Again, your local bonsai club should be able to help you.
Bill Valvanis, in Rochester, NY can guide you.