When there is a relocated runway threshold, the PHAK says:
When the threshold is relocated, the closed portion of the runway is not available for use by aircraft for takeoff or landing, but it is available for taxi.
When does taxiing become become taking off? Can I apply takeoff power before reaching the relocated threshold so long as I don't rotate until past the threshold? If not, is there a maximum permissible speed and/or power I should maintain until that point?