Would this work?: Replace one of the old breakers with a twin breaker. The old wire that went to the old breaker now goes to one of the two outputs of the twin. The other output is avaliable for a new circuit. This should keep the old wire on the same phase. Then repeat for additional breakers. Once you're done with this you'd have a few twin breakers all with an old wire connected and all with avaliable outputs for new circuits. Do one at a time so the wires don't get mixed up. This should maintain proper phasing so the edison hookups stay correct. You won't know if you had to worry about this on all the circuits, but you'd save time spent on hunting them down, and still know that you didn't mess any up.
Does the panel have alternating phases on adjacent slots? If you move an existing breaker an even number of slots down, it should see the same phase. (assuming 120/240V house setup, not 3 phase). Thus you should be able to move 1 breaker to make room for a twin where the panel expects it.
You could measure the voltages on each circuit, make notes as to which read say 0V from the red feeder and which read 240V from the red feeder. Then when you finish moving things retake the readings and compare against your notes.
[This message has been edited by wa2ise (edited 03-01-2005).]
