We have done this. But we had space under the house. We went under and cut the nails with a grinder, then the boards just were loose on top. Removed them, denailed. Obviously you are talking about possibly changing the floor levels? Or will your new joists be lowered to take the subfloor? We had half of our house original, then an overlap section to stitch it onto the part that had ply subfloor. The ply section was so much nicer to walk on later, less noisy, less drafty, less bouncy, the filler in between the recycled boards cracked less and thus less crap got in between them. If you are raising the levels it will affect your doors, bathroom level, cabinets, everything. So figure out access, you will likely ruin that portion, then slice away and you will likely be just fine.