For gosh sakes, don't do this, it's about the worst thing you could do!
You'd be throwing away all the movement for a stubby trunk with no transition whatsoever. Better stick with the movement and grace and work out a more graceful transition.
Maybe this, but never that!
Start a thread graft through the trunk Point A and establish it before you make the cut marked at A
Branch B is useless to the design. It grew much to quickly and has no movement to speak of. Cut at B. You can use the resulting shoot to develop a tapering branch there, or use one of the lower buds that it already has.
This technique (slanted cut on a trunk with movement but little taper and thread grafted branches) is exactly how
this tree was developed.
You can make the actual cut at A about a half inch lower than shown. It's an oblique cut, not a perpendicular one, so it tapers in three dimensions. A hard thing to show in two.
Regards,
Matt