It reminds me of how Reddit allows subs to put in their own stylesheets. Each sub can change the look, placement, and existence of just about every UI element. It makes for the most inconsistent interface I've ever seen for a website.
Although I dislike it when people significantly change UI controls.
I have no question that every study of user interface ever published would indicate that buttons changing visual appearance, position, or availability with no predictability several times in a browsing session is a high friction interface.