I have done several rewires of this type and they can be very time consuming. As far as damage to finish--sometimes you have to, but it usually can be avoided. Also we use the old K & T going down to the recepticles as pull wires for the new romex with pretty good luck. The switches are usually a different situation--they mostly had the insullators inside the wall and we drop down chains or rope to pull them in. Be careful when demoing out the old K & T and don't take out more than you can install in a day because it can be difficult to figure out which wire goes where at the end of the day if you need to temporary these circuits for the night. Good Luck.
Justin
