I've had to deal with this a few times and Fred offered some good advice. I prefer to pull the breech plug, clean out the powder, then push the ball through.
Many years ago a friend was doing a re-conversion on a rifle and failed to check to see if it was loaded. He was going to weld the touch hole area and (with the barrel off the gun and in his vice) when he put the welder to the metal, POW, it went off and shot a hole in his basement wall. That was a mistake he never made again.
FK