I think the stress level OR pleasure level as a result of tank ornament changes, varies according the specific fish and their specie and personality.
For example, I have a freshwater tank with 2 adult oscars. One of my Oscars is blind or almost blind. For them, I very rarely change where their ornaments are placed so she doesn't hurt herself. I do move their things around to thoroughly vacum and clean. But they know this by now from my weekly or bi-weekly water changes I do. They are used to it.
For some of my other tanks, a total tank ornament rearangmenet is almost always a plus for the community. It is often good to break down territories, it can reduce chasing or dominance. It also makes their life more interesting. Plus it's fun to do it. So in short, my answer is - it depends upon the tank and the inhabitants.
Some of my tanks, I rarely change decor or placement. In other tanks, I do make decor changes somehow at least every other water change.
I also think it is important that when you do make a decor change, you should remove all of the ornaments to replace them with different ones. If I want to put a different ornament in, I will remove one and add a new. Never all at the same time, that causes stress. However, if I don't remove any ornaments, I have in some tanks totally re-aranged placement of the ornaments they are used to. The scent is there.
Maybe I psycho analyse my communities too much. But, I do what works for each of my 9 fish tanks. 6 fresh water and 3 salt.