Final answer:
A lifter can change their third attempt deadlift before the bar is loaded and the head referee signals the bar is ready for their third attempt. Changes cannot be made anytime during the lift or after the referee's call.
Step-by-step explanation:
A lifter can change their third attempt deadlift before the start of their third attempt, up until the time the bar is loaded for their attempt and the head referee signals that the bar is ready. You cannot change your attempt anytime during the lift, before your first attempt, before the referee's call, or after the lift is completed. It is important to be strategic and follow the rules to ensure a successful and official lift in powerlifting competitions.