This is really only cost practical with the top tube height (frame size). And if the height reduction is enough then there's no need to take apart lugs/pull out tubes. Pretty much the same as replacing a tube except the disassembly goes quicker. Just a quick hack saw cut just below the upper head lug and the seat lug, only the seat stays will need pulling off.

I have done this once before. I had started building a frame for a, then, friend. He was very short torsoed and had no upper body flexibility. So while the height was about a 60cm the top tube was only 56.5. After the seat stay attachment I cracked the ST when center punching the binder slot's stress relief hole (ironic, I know). I had well over heated the thin ST between the lug then the SS brazing steps. How I dealt with my "friend" is another thread. But after that I cut off the TT and SS as described above. Then I installed a new TT, seat and head lugs and SS. Learning from the first mistake the results were far better. Now I had a 56cm ST size with a 56.5cm TT frame. Found a buyer and he enjoyed his bike for many thousands of miles and years.

In this case the keel of the bike remained the same, the CS, DT, HT and most of the ST all were unchanged angle and lengths. Andy.