Greetings,
Hmm, for the amount of trouble, effort, and risk being considered for purely cosmetic reasons, it seems like less trouble to polish the pins that are already in there.
Regards,

I routinely replace bass hitches with vertical hitches, especially in short pianos like the M. The vertical hitch pins are either stainless split pins or stainless dowel pins.

Removing the blind hole bass pins never really works very well from above. I shear them off, grind everything flush,redrill the plate, moving the the hole back tangent to the the old pin if room.

I've also redrilled the existing holes if they were straight drilled to start with. In either case, for me, its drilled at the Bridgeport, drilled with 1 bit .10" shy of the final dimension, then reamed with a second pass to the final hole dim.

Just getting the existing pin out can also be done by carefully making a pattern and hand drilling from below, then punching the pin out from below...but your template has to be right on.

The longbridge pins should come out easily by punching out from the underside of the plate...assuming they are through drilled.
Jim Ialeggio

Our tech is in the midst of a restoration on a Steinway M. ...