I might be missing something obvious (as it happens often). When I add a TOC I lose access to the top right wrench menu, so I cannot pin/unpin a topic (using for some long event pages).
So the only way to change is to temporarily remove the TOC to access the button.?
Yes, you are looking at the wrong wrench. The second screenshot you provided is of the post admin wrench, at the bottom of every post. There is another admin wrench in the topic menu at the very bottom, before suggested topics.