Yes, the fastest way to disconnect a head from a strung body is to pull the head or a leg away from the body and cut the elastic (and please note that you do not need to heat the head to do this – in fact heating the head and then putting enough pressure on it to pull it away from the neck far enough to see the elastic is probably a bad idea!) But in doing so you will inevitably render the remaining ol’ body useless. If you instead pull the (cold) head away from the neck and take the time to unhook the head hook from the elastic (this will require a hemostat to hold the elastic and probably a pair of pliers to open the hook) and then slip something through the loop in the elastic, like a clean nail, to hold the elastic loop, still entire, at the top of the neck -- some day you, or someone else, might use this ol’ body for another exciting project! (Also, this will maintain the position of the white tube inside the body that the elastic runs through, another good thing to keep.)
(The photo to the right shows body elastic temporarily "anchored" in this manner with a nail. I run the nail through a plastic coffee stirrer to help prevent any possible rust stains from the nail. This photo is of a bjd body, hence there are two loops of elastic - you will only have to deal with one loop in an ol' Tonner body.)
So isn’t it almost as easy to not cut the elastic, and instead go to the small amount of work to unhook it and save that now headless ol’ body for an as yet unknown project in the future??? R.