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?

I don´t think it´s possible but first of all - you woudln´t want 2 branches coming out from the trunk at the same place in bonsai anyway.

Mimo wrote: I don´t think it´s possible but first of all - you woudln´t want 2 branches coming out from the trunk at the same place in bonsai anyway.

Of course, you'd want to thread the branch at an angle of maybe 30 degrees or so..... and not through dead centre of the trunk either. That way it (they) won't be level or perpendicular. Something like this: