There’s a huge difference between taking surplus furniture or swapping sofas and taking down a light fixture and painting it. The sofas can be swapped back easily. That light fixture has been painted, even if they put it back, it’s not the same.
I know that homeowners agree that everything in the room to be redecorated is fair game for changes unless specifically marked otherwise. But the same doesn’t apply to the rest of the house, according to everything I’ve read about the Trading Spaces - Homeowner agreement.
What if I had a beloved family treasure in my bedroom that was the target room, and in accordance with instructions from the Trading Spaces people, moved it out of my room so it wouldn’t be touched, then Doug went, found it in my kitchen and decided to paint it and include it in my room? I’d have done what I was told was necessary to avoid having it damaged but they overrode their prior agreement and damaged it anyway. Unless Doug had some knowledge obtained off-air that said that fixture wasn’t a big deal, he had no way of knowing how the homeowners felt about it.