A gunsmith certainly can eliminate the freebore. It would take a custom ground reamer for the job. If you remove the Freebore, your chamber pressure will rise. Factory shells may not fit the gun, (bullet will crush into the riflings) cause exsesive pressure build up. You will see an increase in accuracy over a standard chamber. But the whole theory with WBY was to shoot fast, more knock down power. I had a chance to visit with Roy WBY in the late 70's. Seemed the justification was to drive a lighter bullet as fast as you could. Use a heavier bullet and slow it down, your accuracy will be the payback. High BC bullets don't have them little parachutes that come out.
Just my .02 little experience too.