annectoo
Yes--I have done it. Twice. I did not read anything online about it or consult any great poinsettia oracles so my experience may not be worth much.
The first time I butchered the plant, (cut it back approximately half all over in the spring) it did well to recover and made many new leaves and what would have been new branches... if I hadn't killed it, which I did, by failing to water it after I moved it outside...
The second time, I had another that I kept watered, so it lived. It literally became a shrub poinsettia that consumed too much of my sun room to put up with after a while so I eventually pitched it.
My method?
in a word--madness--I just took the pruners and cut everything back to some leaf axils about the height I wanted. I lost a few little wimpy stems, but that didn't matter in the end
Perhaps a real sage will step in with some decent advice for you soon
