As a longtime student of frame building and an infrequent builder (31 to date and losing!) I am most admiring of builders who can successfully repair frames by "pulling " apart lugs and keeping everything more or less intact. This is MUCH more difficult than building a new frame. In fact, frame repair in general is a real pain and time sink....
As Phil said, first the assembly pins must be dealt with.
In the CR list we recently touched upon the technique of hearth brazing rather than a hand held torch.. This is a case in which the entire joint, all of the lug and tube ends, are heated uniformly and the joining material (brass/bronze?) is more or less molten at the same time... This overall heating is what must be achieved to successfully disassemble a lugged joint. The builder (un-builder?) cannot use a hand held torch and heat one side then the other to pull the parts away effectively. I remember Mike Melton recommending a "rosette" head for the torch to try to heat the whole joint.. I have also seen a double headed torch with one head & flame on opposite sides used. Even with these devises, it takes a heck of a lot of talent to get the joint apart with frying the lug tips, etc.
After the lugs are "freed" they are usually messy with uneven blobs of brass in and out and much clean up is necessary to have a nice piece with which to start building again.....
Dale Brown
Greensboro, North Carolina