Once a thread graft has fully and truly succeeded, will the “entry” side of the scion reverse its direction of growth (and survive) if you cut it ‘long’ thus creating two branches for the price of a single graft?
That idea won't work. Plants "know" which end is which. The scion will grow a bigger branch from one end and roots from the other end, if it is in the right environment - i.e. if the base of the scion is in some soil.
Your idea is used to graft on new roots, but that isn't what you wanted to do.
If you got lucky, a bud on the other end of your graft might grow into a branch, but it probably wouldn't be very strong, and it certainly wouldn't grow pointing "outwards" from the trunk that you grafted it onto.